diff --git a/src/components/chat/AgentActivityTimeline.test.tsx b/src/components/chat/AgentActivityTimeline.test.tsx
new file mode 100644
index 0000000..35b9e93
--- /dev/null
+++ b/src/components/chat/AgentActivityTimeline.test.tsx
@@ -0,0 +1,69 @@
+import "@testing-library/jest-dom";
+import { fireEvent, render, screen } from "@testing-library/react";
+
+import { AgentActivityTimeline } from "./AgentActivityTimeline";
+
+describe("AgentActivityTimeline", () => {
+  it("shows only the first lines of a long tool command until expanded", () => {
+    const target = [
+      "cd /app/data/conversation-workspaces/conversation-example",
+      "python3 - <<'EOF'",
+      "import json, glob",
+      "print('fourth line')",
+      "EOF",
+    ].join("\n");
+    render(
+      <AgentActivityTimeline
+        activities={[
+          {
+            id: "analysis",
+            title: "处理分析数据",
+            reason: "正在核查结果。",
+            status: "completed",
+            startedAt: 1000,
+            endedAt: 2000,
+            actions: [
+              {
+                id: "long-command",
+                tool: "bash",
+                title: "运行本地分析",
+                status: "completed",
+                target,
+                startedAt: 1100,
+                endedAt: 1900,
+              },
+              {
+                id: "short-command",
+                tool: "tjwater_cli",
+                title: "查询后端数据",
+                status: "completed",
+                target: "help data",
+                startedAt: 1900,
+                endedAt: 1950,
+              },
+            ],
+          },
+        ]}
+      />,
+    );
+
+    fireEvent.click(screen.getByRole("button", { name: "展开分析过程" }));
+    expect(screen.getByText(/import json, glob/u)).toBeInTheDocument();
+    expect(screen.queryByText(/fourth line/u)).not.toBeInTheDocument();
+    expect(screen.getByText("help data")).toBeInTheDocument();
+    expect(screen.getByRole("button", { name: "展开完整内容" })).toHaveAttribute(
+      "aria-expanded",
+      "false",
+    );
+
+    fireEvent.click(screen.getByRole("button", { name: "展开完整内容" }));
+    expect(screen.getByText(/fourth line/u)).toBeInTheDocument();
+    expect(screen.getByRole("button", { name: "收起内容" })).toHaveAttribute(
+      "aria-expanded",
+      "true",
+    );
+
+    fireEvent.click(screen.getByRole("button", { name: "收起内容" }));
+    expect(screen.queryByText(/fourth line/u)).not.toBeInTheDocument();
+  });
+});
diff --git a/src/components/chat/AgentActivityTimeline.tsx b/src/components/chat/AgentActivityTimeline.tsx
index de91ba3..e685cfb 100644
--- a/src/components/chat/AgentActivityTimeline.tsx
+++ b/src/components/chat/AgentActivityTimeline.tsx
@@ -3,6 +3,7 @@
 import React, { useEffect, useMemo, useState } from "react";
 import {
   Box,
+  Button,
   Collapse,
   IconButton,
   LinearProgress,
@@ -89,6 +90,11 @@ const ActionStatusIcon = ({ status }: { status: AgentActivityAction["status"] })
 
 const ActionRow = ({ action, now }: { action: AgentActivityAction; now: number }) => {
   const elapsed = getElapsedMs(action, now);
+  const [targetExpanded, setTargetExpanded] = useState(false);
+  const targetId = React.useId();
+  const target = action.target ?? "";
+  const targetPreview = target.split(/\r?\n/u).slice(0, 3).join("\n").slice(0, 240);
+  const hasLongTarget = targetPreview.length < target.length;
   return (
     <Stack
       direction="row"
@@ -111,19 +117,45 @@ const ActionRow = ({ action, now }: { action: AgentActivityAction; now: number }
           </Typography>
         </Stack>
         {action.target ? (
-          <Typography
-            variant="caption"
-            color="text.secondary"
-            sx={{
-              display: "block",
-              mt: 0.2,
-              fontFamily: "monospace",
-              wordBreak: "break-word",
-              whiteSpace: "pre-wrap",
-            }}
-          >
-            {action.target}
-          </Typography>
+          <Box sx={{ mt: 0.2 }}>
+            <Typography
+              id={targetId}
+              variant="caption"
+              color="text.secondary"
+              sx={{
+                display: !targetExpanded && hasLongTarget ? "-webkit-box" : "block",
+                fontFamily: "monospace",
+                overflow: !targetExpanded && hasLongTarget ? "hidden" : "visible",
+                overflowWrap: "anywhere",
+                whiteSpace: "pre-wrap",
+                ...(!targetExpanded && hasLongTarget
+                  ? { WebkitBoxOrient: "vertical", WebkitLineClamp: 3 }
+                  : {}),
+              }}
+            >
+              {targetExpanded ? target : targetPreview}
+            </Typography>
+            {hasLongTarget ? (
+              <Button
+                size="small"
+                aria-controls={targetId}
+                aria-expanded={targetExpanded}
+                onClick={() => setTargetExpanded((current) => !current)}
+                sx={{
+                  mt: 0.2,
+                  p: 0,
+                  minWidth: 0,
+                  color: activityAccent,
+                  fontSize: "0.75rem",
+                  fontWeight: 650,
+                  lineHeight: 1.5,
+                  textTransform: "none",
+                }}
+              >
+                {targetExpanded ? "收起内容" : "展开完整内容"}
+              </Button>
+            ) : null}
+          </Box>
         ) : null}
         {action.error ? (
           <Typography