diff --git a/src/commands/backup.atomic.test.ts b/src/commands/backup.atomic.test.ts
new file mode 100644
index 00000000000..4f16634eacb
--- /dev/null
+++ b/src/commands/backup.atomic.test.ts
@@ -0,0 +1,62 @@
+import fs from "node:fs/promises";
+import os from "node:os";
+import path from "node:path";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { createTempHomeEnv, type TempHomeEnv } from "../test-utils/temp-home.js";
+
+const tarCreateMock = vi.hoisted(() => vi.fn());
+const backupVerifyCommandMock = vi.hoisted(() => vi.fn());
+
+vi.mock("tar", () => ({
+  c: tarCreateMock,
+}));
+
+vi.mock("./backup-verify.js", () => ({
+  backupVerifyCommand: backupVerifyCommandMock,
+}));
+
+const { backupCreateCommand } = await import("./backup.js");
+
+describe("backupCreateCommand atomic archive write", () => {
+  let tempHome: TempHomeEnv;
+
+  beforeEach(async () => {
+    tempHome = await createTempHomeEnv("openclaw-backup-atomic-test-");
+    tarCreateMock.mockReset();
+    backupVerifyCommandMock.mockReset();
+  });
+
+  afterEach(async () => {
+    await tempHome.restore();
+  });
+
+  it("does not leave a partial final archive behind when tar creation fails", async () => {
+    const stateDir = path.join(tempHome.home, ".openclaw");
+    const archiveDir = await fs.mkdtemp(path.join(os.tmpdir(), "openclaw-backup-failure-"));
+    try {
+      await fs.writeFile(path.join(stateDir, "openclaw.json"), JSON.stringify({}), "utf8");
+      await fs.writeFile(path.join(stateDir, "state.txt"), "state\n", "utf8");
+
+      tarCreateMock.mockRejectedValueOnce(new Error("disk full"));
+
+      const runtime = {
+        log: vi.fn(),
+        error: vi.fn(),
+        exit: vi.fn(),
+      };
+      const outputPath = path.join(archiveDir, "backup.tar.gz");
+
+      await expect(
+        backupCreateCommand(runtime, {
+          output: outputPath,
+        }),
+      ).rejects.toThrow(/disk full/i);
+
+      await expect(fs.access(outputPath)).rejects.toThrow();
+      const remaining = await fs.readdir(archiveDir);
+      expect(remaining).toEqual([]);
+    } finally {
+      await fs.rm(archiveDir, { recursive: true, force: true });
+    }
+  });
+});
diff --git a/src/commands/backup.ts b/src/commands/backup.ts
index b1fc2f1ad50..5e344dc640e 100644
--- a/src/commands/backup.ts
+++ b/src/commands/backup.ts
@@ -1,3 +1,4 @@
+import { randomUUID } from "node:crypto";
 import fs from "node:fs/promises";
 import os from "node:os";
 import path from "node:path";
@@ -119,6 +120,10 @@ async function assertOutputPathReady(outputPath: string): Promise<void> {
   }
 }
 
+function buildTempArchivePath(outputPath: string): string {
+  return `${outputPath}.${randomUUID()}.tmp`;
+}
+
 async function canonicalizePathForContainment(targetPath: string): Promise<string> {
   const resolved = path.resolve(targetPath);
   try {
@@ -265,6 +270,7 @@ export async function backupCreateCommand(
     await fs.mkdir(path.dirname(outputPath), { recursive: true });
     const tempDir = await fs.mkdtemp(path.join(os.tmpdir(), "openclaw-backup-"));
     const manifestPath = path.join(tempDir, "manifest.json");
+    const tempArchivePath = buildTempArchivePath(outputPath);
     try {
       const manifest = buildManifest({
         createdAt,
@@ -281,7 +287,7 @@ export async function backupCreateCommand(
 
       await tar.c(
         {
-          file: outputPath,
+          file: tempArchivePath,
           gzip: true,
           portable: true,
           preservePaths: true,
@@ -295,7 +301,9 @@ export async function backupCreateCommand(
         },
         [manifestPath, ...result.assets.map((asset) => asset.sourcePath)],
       );
+      await fs.rename(tempArchivePath, outputPath);
     } finally {
+      await fs.rm(tempArchivePath, { force: true }).catch(() => undefined);
       await fs.rm(tempDir, { recursive: true, force: true }).catch(() => undefined);
     }