diff --git a/.env.example b/.env.example
index bd299f0..635cfa2 100644
--- a/.env.example
+++ b/.env.example
@@ -42,6 +42,11 @@ GPTMAIL_API_KEY=gpt-test
 # 注意：若填写此处，docker-compose.yml 中 watchtower 服务会自动同步读取同一变量
 WATCHTOWER_HTTP_API_TOKEN=
 
+# Watchtower Docker API 版本覆盖项。
+# 默认留空，让 Watchtower/Docker SDK 自动协商 API 版本。
+# 仅当 Docker 29.0-29.2 报 client version too old 时取消注释并设为 1.44。
+# WATCHTOWER_DOCKER_API_VERSION=1.44
+
 # Docker API 自更新（可选，高级功能）
 # ⚠️ 警告：启用后容器可通过 Docker API 控制宿主机其他容器，存在安全风险
 # 需同时取消 docker-compose.yml 中 docker.sock 挂载的注释
diff --git a/README.en.md b/README.en.md
index b0f3d94..a86a72f 100644
--- a/README.en.md
+++ b/README.en.md
@@ -183,6 +183,9 @@ services:
       - WATCHTOWER_HTTP_API_TOKEN=${WATCHTOWER_HTTP_API_TOKEN:-outlook-mail-plus-watchtower-default}
       - WATCHTOWER_HTTP_API_UPDATE=true
       - WATCHTOWER_CLEANUP=true
+      # Optional: set WATCHTOWER_DOCKER_API_VERSION=1.44 in .env if Docker 29.0-29.2 reports client version too old
+      # Empty by default to keep Docker API negotiation and avoid forcing too-new API versions on older engines
+      - DOCKER_API_VERSION=${WATCHTOWER_DOCKER_API_VERSION:-}
       - WATCHTOWER_HTTP_API_PERIODIC_POLLS=false
     command: --http-api-update --label-enable
     labels:
@@ -209,12 +212,12 @@ Notes:
 3. Switch "Update Method" to "Docker API" in Settings
 4. ⚠️ Please fully understand the security implications before enabling
 
-> ⚠️ **Troubleshooting**: If you see `client version 1.25 is too old. Minimum supported API version is 1.44` in Watchtower logs, your local Watchtower image cache is stale (the embedded Docker client API is too old). Fix:
+> ⚠️ **Troubleshooting**: If you see `client version 1.25 is too old. Minimum supported API version is 1.44` in Watchtower logs, Docker Engine requires a newer Docker API version than Watchtower's default client API. To avoid breaking older Docker Engines, `docker-compose.yml` keeps the override empty by default. Set `WATCHTOWER_DOCKER_API_VERSION=1.44` in `.env`, then run:
 > ```bash
-> docker compose pull watchtower    # Pull the latest image
-> docker compose up -d watchtower   # Recreate the container
+> docker compose pull watchtower    # Pull the image
+> docker compose up -d watchtower   # Recreate with the new config
 > ```
-> The `docker-compose.yml` in this repo has pinned Watchtower to `1.7.1` to prevent this issue.
+> If you are still on Docker 24 or older, do not set this override, or set it to an API version supported by that engine.
 
 #### ClawCloud / Reverse Proxy Deployment Notes
 
@@ -275,6 +278,8 @@ python -m unittest discover -s tests -v
   Watchtower API auth token. **Can be left empty** — both app and watchtower automatically use the same built-in default, making it work out of the box; for production, use a random strong password
 - `WATCHTOWER_API_URL`
   Watchtower API address, default `http://watchtower:8080` (Docker internal network, usually no need to change)
+- `WATCHTOWER_DOCKER_API_VERSION`
+  Optional Docker API version override for Watchtower. Default: empty, preserving API negotiation; set to `1.44` only if Docker 29.0-29.2 reports `client version too old`
 - `DOCKER_SELF_UPDATE_ALLOW`
   Whether to enable Docker API self-update, default `false`. ⚠️ Grants container Docker API access when enabled
 - `DOCKER_IMAGE`
diff --git a/README.md b/README.md
index 62475b2..d011184 100644
--- a/README.md
+++ b/README.md
@@ -188,6 +188,9 @@ services:
       - WATCHTOWER_HTTP_API_TOKEN=${WATCHTOWER_HTTP_API_TOKEN:-outlook-mail-plus-watchtower-default}
       - WATCHTOWER_HTTP_API_UPDATE=true
       - WATCHTOWER_CLEANUP=true
+      # 可选：Docker 29.0-29.2 若报 client version too old，可在 .env 设置 WATCHTOWER_DOCKER_API_VERSION=1.44
+      # 默认留空以保留 Docker API 自动协商，避免旧 Docker Engine 被强制使用过高 API 版本
+      - DOCKER_API_VERSION=${WATCHTOWER_DOCKER_API_VERSION:-}
       - WATCHTOWER_HTTP_API_PERIODIC_POLLS=false
     command: --http-api-update --label-enable
     labels:
@@ -214,12 +217,12 @@ networks:
 3. 在设置页选择"更新方式"为"Docker API"
 4. ⚠️ 请充分了解安全风险后再启用
 
-> ⚠️ **常见问题**：如果 Watchtower 容器日志中出现 `client version 1.25 is too old. Minimum supported API version is 1.44` 错误，说明你本地缓存了旧版 Watchtower 镜像（内嵌的 Docker 客户端 API 版本过旧）。解决方法：
+> ⚠️ **常见问题**：如果 Watchtower 容器日志中出现 `client version 1.25 is too old. Minimum supported API version is 1.44` 错误，说明当前 Docker Engine 要求更高的 Docker API 版本，而 Watchtower 的默认客户端 API 版本偏低。为避免影响旧版 Docker Engine，`docker-compose.yml` 默认保留自动协商；遇到该错误时可在 `.env` 中设置 `WATCHTOWER_DOCKER_API_VERSION=1.44`，然后执行：
 > ```bash
-> docker compose pull watchtower    # 拉取最新镜像
-> docker compose up -d watchtower   # 重建容器
+> docker compose pull watchtower    # 拉取镜像
+> docker compose up -d watchtower   # 用新配置重建容器
 > ```
-> 本项目 `docker-compose.yml` 已固定 Watchtower 版本为 `1.7.1`，可避免此类问题。
+> 如果仍使用 Docker 24 或更早版本，请不要设置此覆盖项，或设置为该 Docker Engine 支持的 API 版本。
 
 #### ClawCloud / 反向代理部署注意事项
 
@@ -284,6 +287,8 @@ python -m unittest discover -s tests -v
   Watchtower API 鉴权令牌。**可留空**，留空时 app 和 watchtower 两边自动使用同一内置默认值，开箱即用；生产环境建议设置随机强密码
 - `WATCHTOWER_API_URL`
   Watchtower API 地址，默认 `http://watchtower:8080`（Docker 内部网络，通常无需修改）
+- `WATCHTOWER_DOCKER_API_VERSION`
+  Watchtower Docker API 版本覆盖项。默认留空，保留 API 自动协商；仅当 Docker 29.0-29.2 出现 `client version too old` 时建议设为 `1.44`
 - `DOCKER_SELF_UPDATE_ALLOW`
   是否启用 Docker API 自更新功能，默认 `false`。⚠️ 启用后容器可访问 Docker API，存在安全风险
 - `DOCKER_IMAGE`
diff --git a/docker-compose.yml b/docker-compose.yml
index ed1b655..09d3475 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -85,6 +85,9 @@ services:
       - WATCHTOWER_HTTP_API_TOKEN=${WATCHTOWER_HTTP_API_TOKEN:-outlook-mail-plus-watchtower-default}
       - WATCHTOWER_HTTP_API_UPDATE=true
       - WATCHTOWER_CLEANUP=true
+      # 可选：Docker 29.0-29.2 若报 client version too old，可在 .env 设置 WATCHTOWER_DOCKER_API_VERSION=1.44
+      # 默认留空以保留 Docker API 自动协商，避免旧 Docker Engine 被强制使用过高 API 版本
+      - DOCKER_API_VERSION=${WATCHTOWER_DOCKER_API_VERSION:-}
       # 禁用定时轮询，仅通过界面触发更新
       - WATCHTOWER_HTTP_API_PERIODIC_POLLS=false
     command: --http-api-update --label-enable
diff --git a/tests/test_watchtower_compose_contract.py b/tests/test_watchtower_compose_contract.py
new file mode 100644
index 0000000..e397eb8
--- /dev/null
+++ b/tests/test_watchtower_compose_contract.py
@@ -0,0 +1,31 @@
+"""Watchtower compose contract tests."""
+
+from __future__ import annotations
+
+import unittest
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+
+
+class WatchtowerComposeContractTests(unittest.TestCase):
+    def test_compose_keeps_watchtower_docker_api_override_optional(self):
+        content = (REPO_ROOT / "docker-compose.yml").read_text(encoding="utf-8")
+        self.assertIn("DOCKER_API_VERSION=${WATCHTOWER_DOCKER_API_VERSION:-}", content)
+        self.assertNotIn("DOCKER_API_VERSION=${WATCHTOWER_DOCKER_API_VERSION:-1.44}", content)
+
+    def test_readme_snippets_keep_watchtower_docker_api_override_optional(self):
+        for path in ("README.md", "README.en.md"):
+            with self.subTest(path=path):
+                content = (REPO_ROOT / path).read_text(encoding="utf-8")
+                self.assertIn("DOCKER_API_VERSION=${WATCHTOWER_DOCKER_API_VERSION:-}", content)
+                self.assertNotIn("DOCKER_API_VERSION=${WATCHTOWER_DOCKER_API_VERSION:-1.44}", content)
+
+    def test_env_example_documents_watchtower_docker_api_override(self):
+        content = (REPO_ROOT / ".env.example").read_text(encoding="utf-8")
+        self.assertIn("WATCHTOWER_DOCKER_API_VERSION=1.44", content)
+        self.assertIn("默认留空", content)
+
+
+if __name__ == "__main__":
+    unittest.main()