diff --git a/web/src/pages/flow/canvas/index.tsx b/web/src/pages/flow/canvas/index.tsx
index b3010995c..b1f4864e9 100644
--- a/web/src/pages/flow/canvas/index.tsx
+++ b/web/src/pages/flow/canvas/index.tsx
@@ -20,9 +20,16 @@ import {
 import { RagNode } from './node';
 
 import ChatDrawer from '../chat/drawer';
+import { isValidConnection } from '../utils';
 import styles from './index.less';
+import { BeginNode } from './node/begin-node';
+import { CategorizeNode } from './node/categorize-node';
 
-const nodeTypes = { ragNode: RagNode };
+const nodeTypes = {
+  ragNode: RagNode,
+  categorizeNode: CategorizeNode,
+  beginNode: BeginNode,
+};
 
 const edgeTypes = {
   buttonEdge: ButtonEdge,
@@ -76,6 +83,7 @@ function FlowCanvas({ chatDrawerVisible, hideChatDrawer }: IProps) {
         onKeyUp={handleKeyUp}
         onSelectionChange={onSelectionChange}
         nodeOrigin={[0.5, 0]}
+        isValidConnection={isValidConnection}
         onChange={(...params) => {
           console.info('params:', ...params);
         }}
diff --git a/web/src/pages/flow/canvas/node/begin-node.tsx b/web/src/pages/flow/canvas/node/begin-node.tsx
new file mode 100644
index 000000000..badcfcd56
--- /dev/null
+++ b/web/src/pages/flow/canvas/node/begin-node.tsx
@@ -0,0 +1,39 @@
+import { Flex, Space } from 'antd';
+import classNames from 'classnames';
+import { Handle, NodeProps, Position } from 'reactflow';
+import { Operator } from '../../constant';
+import { NodeData } from '../../interface';
+import OperatorIcon from '../../operator-icon';
+import NodeDropdown from './dropdown';
+
+import styles from './index.less';
+
+// TODO: do not allow other nodes to connect to this node
+export function BeginNode({ id, data, selected }: NodeProps<NodeData>) {
+  return (
+    <section
+      className={classNames(styles.ragNode, {
+        [styles.selectedNode]: selected,
+      })}
+    >
+      <Handle
+        type="source"
+        position={Position.Right}
+        isConnectable
+        className={styles.handle}
+      ></Handle>
+      <Flex vertical align="center" justify="center">
+        <Space size={6}>
+          <OperatorIcon
+            name={data.label as Operator}
+            fontSize={16}
+          ></OperatorIcon>
+          <NodeDropdown id={id}></NodeDropdown>
+        </Space>
+      </Flex>
+      <section className={styles.bottomBox}>
+        <div className={styles.nodeName}>{id}</div>
+      </section>
+    </section>
+  );
+}
diff --git a/web/src/pages/flow/canvas/node/categorize-node.tsx b/web/src/pages/flow/canvas/node/categorize-node.tsx
new file mode 100644
index 000000000..397adfe75
--- /dev/null
+++ b/web/src/pages/flow/canvas/node/categorize-node.tsx
@@ -0,0 +1,51 @@
+import { Flex, Space } from 'antd';
+import classNames from 'classnames';
+import get from 'lodash/get';
+import { Handle, NodeProps, Position } from 'reactflow';
+import { CategorizeAnchorPointPositions, Operator } from '../../constant';
+import { NodeData } from '../../interface';
+import OperatorIcon from '../../operator-icon';
+import CategorizeHandle from './categorize-handle';
+import NodeDropdown from './dropdown';
+
+import styles from './index.less';
+
+export function CategorizeNode({ id, data, selected }: NodeProps<NodeData>) {
+  const categoryData = get(data, 'form.category_description') ?? {};
+
+  return (
+    <section
+      className={classNames(styles.ragNode, {
+        [styles.selectedNode]: selected,
+      })}
+    >
+      <Handle
+        type="target"
+        position={Position.Left}
+        isConnectable
+        className={styles.handle}
+      ></Handle>
+      {Object.keys(categoryData).map((x, idx) => (
+        <CategorizeHandle
+          top={CategorizeAnchorPointPositions[idx].top}
+          right={CategorizeAnchorPointPositions[idx].right}
+          key={idx}
+          text={x}
+          idx={idx}
+        ></CategorizeHandle>
+      ))}
+      <Flex vertical align="center" justify="center">
+        <Space size={6}>
+          <OperatorIcon
+            name={data.label as Operator}
+            fontSize={16}
+          ></OperatorIcon>
+          <NodeDropdown id={id}></NodeDropdown>
+        </Space>
+      </Flex>
+      <section className={styles.bottomBox}>
+        <div className={styles.nodeName}>{id}</div>
+      </section>
+    </section>
+  );
+}
diff --git a/web/src/pages/flow/canvas/node/dropdown.tsx b/web/src/pages/flow/canvas/node/dropdown.tsx
new file mode 100644
index 000000000..632a60583
--- /dev/null
+++ b/web/src/pages/flow/canvas/node/dropdown.tsx
@@ -0,0 +1,47 @@
+import OperateDropdown from '@/components/operate-dropdown';
+import { CopyOutlined } from '@ant-design/icons';
+import { Flex, MenuProps } from 'antd';
+import { useCallback } from 'react';
+import { useTranslation } from 'react-i18next';
+import useGraphStore from '../../store';
+
+interface IProps {
+  id: string;
+}
+
+const NodeDropdown = ({ id }: IProps) => {
+  const { t } = useTranslation();
+  const deleteNodeById = useGraphStore((store) => store.deleteNodeById);
+  const duplicateNodeById = useGraphStore((store) => store.duplicateNode);
+
+  const deleteNode = useCallback(() => {
+    deleteNodeById(id);
+  }, [id, deleteNodeById]);
+
+  const duplicateNode = useCallback(() => {
+    duplicateNodeById(id);
+  }, [id, duplicateNodeById]);
+
+  const items: MenuProps['items'] = [
+    {
+      key: '2',
+      onClick: duplicateNode,
+      label: (
+        <Flex justify={'space-between'}>
+          {t('common.copy')}
+          <CopyOutlined />
+        </Flex>
+      ),
+    },
+  ];
+
+  return (
+    <OperateDropdown
+      iconFontSize={14}
+      deleteItem={deleteNode}
+      items={items}
+    ></OperateDropdown>
+  );
+};
+
+export default NodeDropdown;
diff --git a/web/src/pages/flow/canvas/node/index.tsx b/web/src/pages/flow/canvas/node/index.tsx
index 5d0fc1bda..67336c37c 100644
--- a/web/src/pages/flow/canvas/node/index.tsx
+++ b/web/src/pages/flow/canvas/node/index.tsx
@@ -1,17 +1,13 @@
 import classNames from 'classnames';
 import { Handle, NodeProps, Position } from 'reactflow';
 
-import OperateDropdown from '@/components/operate-dropdown';
-import { CopyOutlined } from '@ant-design/icons';
-import { Flex, MenuProps, Space } from 'antd';
+import { Flex, Space } from 'antd';
 import get from 'lodash/get';
-import { useCallback } from 'react';
-import { useTranslation } from 'react-i18next';
 import { CategorizeAnchorPointPositions, Operator } from '../../constant';
 import { NodeData } from '../../interface';
 import OperatorIcon from '../../operator-icon';
-import useGraphStore from '../../store';
 import CategorizeHandle from './categorize-handle';
+import NodeDropdown from './dropdown';
 import styles from './index.less';
 
 export function RagNode({
@@ -20,34 +16,9 @@ export function RagNode({
   isConnectable = true,
   selected,
 }: NodeProps<NodeData>) {
-  const { t } = useTranslation();
-  const deleteNodeById = useGraphStore((store) => store.deleteNodeById);
-  const duplicateNodeById = useGraphStore((store) => store.duplicateNode);
-
-  const deleteNode = useCallback(() => {
-    deleteNodeById(id);
-  }, [id, deleteNodeById]);
-
-  const duplicateNode = useCallback(() => {
-    duplicateNodeById(id);
-  }, [id, duplicateNodeById]);
-
   const isCategorize = data.label === Operator.Categorize;
   const categoryData = get(data, 'form.category_description') ?? {};
 
-  const items: MenuProps['items'] = [
-    {
-      key: '2',
-      onClick: duplicateNode,
-      label: (
-        <Flex justify={'space-between'}>
-          {t('common.copy')}
-          <CopyOutlined />
-        </Flex>
-      ),
-    },
-  ];
-
   return (
     <section
       className={classNames(styles.ragNode, {
@@ -86,11 +57,7 @@ export function RagNode({
             name={data.label as Operator}
             fontSize={16}
           ></OperatorIcon>
-          <OperateDropdown
-            iconFontSize={14}
-            deleteItem={deleteNode}
-            items={items}
-          ></OperateDropdown>
+          <NodeDropdown id={id}></NodeDropdown>
         </Space>
       </Flex>
 
diff --git a/web/src/pages/flow/constant.tsx b/web/src/pages/flow/constant.tsx
index fc10b1345..cfe8a0ce0 100644
--- a/web/src/pages/flow/constant.tsx
+++ b/web/src/pages/flow/constant.tsx
@@ -97,3 +97,27 @@ export const CategorizeAnchorPointPositions = [
   { top: 91, right: 20 },
   { top: 98, right: 34 },
 ];
+
+// key is the source of the edge, value is the target of the edge
+// no connection lines are allowed between key and value
+export const RestrictedUpstreamMap = {
+  [Operator.Begin]: [
+    Operator.Begin,
+    Operator.Answer,
+    Operator.Categorize,
+    Operator.Generate,
+    Operator.Retrieval,
+  ],
+  [Operator.Categorize]: [Operator.Begin, Operator.Categorize, Operator.Answer],
+  [Operator.Answer]: [],
+  [Operator.Retrieval]: [],
+  [Operator.Generate]: [],
+};
+
+export const NodeMap = {
+  [Operator.Begin]: 'beginNode',
+  [Operator.Categorize]: 'categorizeNode',
+  [Operator.Retrieval]: 'ragNode',
+  [Operator.Generate]: 'ragNode',
+  [Operator.Answer]: 'ragNode',
+};
diff --git a/web/src/pages/flow/hooks.ts b/web/src/pages/flow/hooks.ts
index bddac12ef..ed41e7b1d 100644
--- a/web/src/pages/flow/hooks.ts
+++ b/web/src/pages/flow/hooks.ts
@@ -25,7 +25,7 @@ import { useDebounceEffect } from 'ahooks';
 import { FormInstance } from 'antd';
 import { humanId } from 'human-id';
 import { useParams } from 'umi';
-import { Operator } from './constant';
+import { NodeMap, Operator } from './constant';
 import useGraphStore, { RFState } from './store';
 import { buildDslComponentsByGraph } from './utils';
 
@@ -87,7 +87,7 @@ export const useHandleDrop = () => {
       });
       const newNode = {
         id: `${type}:${humanId()}`,
-        type: 'ragNode',
+        type: NodeMap[type as Operator] || 'ragNode',
         position: position || {
           x: 0,
           y: 0,
diff --git a/web/src/pages/flow/mock.tsx b/web/src/pages/flow/mock.tsx
index 5b5fda716..af0129ba5 100644
--- a/web/src/pages/flow/mock.tsx
+++ b/web/src/pages/flow/mock.tsx
@@ -38,7 +38,7 @@ export const dsl = {
     nodes: [
       {
         id: 'begin',
-        type: 'ragNode',
+        type: 'beginNode',
         position: {
           x: 50,
           y: 200,
diff --git a/web/src/pages/flow/utils.ts b/web/src/pages/flow/utils.ts
index d84360bd5..f6f50c140 100644
--- a/web/src/pages/flow/utils.ts
+++ b/web/src/pages/flow/utils.ts
@@ -3,9 +3,13 @@ import { removeUselessFieldsFromValues } from '@/utils/form';
 import dagre from 'dagre';
 import { curry, isEmpty } from 'lodash';
 import pipe from 'lodash/fp/pipe';
-import { Edge, MarkerType, Node, Position } from 'reactflow';
+import { Connection, Edge, MarkerType, Node, Position } from 'reactflow';
 import { v4 as uuidv4 } from 'uuid';
-import { Operator, initialFormValuesMap } from './constant';
+import {
+  Operator,
+  RestrictedUpstreamMap,
+  initialFormValuesMap,
+} from './constant';
 import { NodeData } from './interface';
 
 const buildEdges = (
@@ -162,3 +166,14 @@ export const buildDslComponentsByGraph = (
 
   return components;
 };
+
+export const getOperatorType = (id: string | null) => {
+  return id?.split(':')[0] as Operator | undefined;
+};
+
+// restricted lines cannot be connected successfully.
+export const isValidConnection = (connection: Connection) => {
+  return RestrictedUpstreamMap[
+    getOperatorType(connection.source) as Operator
+  ]?.every((x) => x !== getOperatorType(connection.target));
+};