diff --git a/scripts/agent-update.sh b/scripts/agent-update.sh
index e73dc97..f0f13da 100755
--- a/scripts/agent-update.sh
+++ b/scripts/agent-update.sh
@@ -13,15 +13,18 @@ command -v curl >/dev/null || die "缺少 curl"
 tmp_dir="$(mktemp -d /tmp/nexusgate-agent-update.XXXXXX)"
 trap 'rm -rf -- "$tmp_dir"' EXIT
 
-# 按已安装的程序判断实现：Go 二进制优先，其次是旧版 Node agent.js
+# 按已安装的程序判断当前实现：Go 二进制优先，其次是旧版 Node agent.js
 if [[ -x /opt/nexusgate-agent/nexusgate-agent ]]; then
-  AGENT_IMPL="go"
+  CURRENT_IMPL="go"
 elif [[ -f /opt/nexusgate-agent/agent.js ]]; then
-  AGENT_IMPL="node"
+  CURRENT_IMPL="node"
 else
   die "未找到 Agent 程序（/opt/nexusgate-agent/nexusgate-agent 或 agent.js）"
 fi
-info "当前 Agent 实现：${AGENT_IMPL}"
+# 目标实现：更新默认迁移到 Go；显式 NG_AGENT_IMPL=node 时保留 Node
+TARGET_IMPL="go"
+[[ "${NG_AGENT_IMPL:-}" == "node" ]] && TARGET_IMPL="node"
+info "当前 Agent 实现：${CURRENT_IMPL}；更新目标：${TARGET_IMPL}"
 
 raw_fetch() {
   curl -fL --retry 3 "https://raw.githubusercontent.com/${REPO}/${BRANCH}/$1" -o "$2"
@@ -56,7 +59,7 @@ raw_fetch scripts/agent-logrotate.conf "$tmp_dir/logrotate.conf"
 raw_fetch scripts/agent-logrotate-setup.sh "$tmp_dir/logrotate-setup.sh"
 [[ -s "$tmp_dir/update.sh" ]] || die 'Agent 升级脚本下载不完整'
 
-if [[ "$AGENT_IMPL" == "go" ]]; then
+if [[ "$TARGET_IMPL" == "go" ]]; then
   fetch_agent_binary "$tmp_dir/nexusgate-agent"
 else
   raw_fetch agent/agent.js "$tmp_dir/agent.js"
@@ -68,14 +71,14 @@ fi
 # before the running process is replaced.
 (
   set -a; source /etc/nexusgate/agent.env; set +a
-  if [[ "$AGENT_IMPL" == "go" ]]; then
+  if [[ "$CURRENT_IMPL" == "go" ]]; then
     /opt/nexusgate-agent/nexusgate-agent flush-usage
   else
     node /opt/nexusgate-agent/agent.js flush-usage
   fi
 ) || die '更新前流量统计上报失败，保留原 Agent；检查控制面连接和 ng-agent doctor 后重试'
 
-if [[ "$AGENT_IMPL" == "go" ]]; then
+if [[ "$TARGET_IMPL" == "go" ]]; then
   install -m 0755 "$tmp_dir/nexusgate-agent" /opt/nexusgate-agent/nexusgate-agent
 else
   install -m 0644 "$tmp_dir/agent.js" /opt/nexusgate-agent/agent.js
@@ -112,7 +115,7 @@ if command -v systemctl >/dev/null && [[ -d /run/systemd/system ]]; then
   raw_fetch systemd/nexusgate-sing-box.service "$tmp_dir/nexusgate-sing-box.service"
   install -m 0644 "$tmp_dir/nexusgate-agent.service" /etc/systemd/system/nexusgate-agent.service
   install -m 0644 "$tmp_dir/nexusgate-sing-box.service" /etc/systemd/system/nexusgate-sing-box.service
-  if [[ "$AGENT_IMPL" == "node" ]]; then
+  if [[ "$TARGET_IMPL" == "node" ]]; then
     # 仓库里的 unit 默认指向 Go 二进制；Node 实现改为经 run.sh 启动
     sed -i 's|^ExecStart=.*|ExecStart=/opt/nexusgate-agent/run.sh|' /etc/systemd/system/nexusgate-agent.service
   fi
@@ -125,7 +128,7 @@ elif command -v rc-service >/dev/null; then
   raw_fetch openrc/nexusgate-sing-box "$tmp_dir/openrc-sing-box"
   install -m 0755 "$tmp_dir/openrc-agent" /etc/init.d/nexusgate-agent
   install -m 0755 "$tmp_dir/openrc-sing-box" /etc/init.d/nexusgate-sing-box
-  if [[ "$AGENT_IMPL" == "node" ]]; then
+  if [[ "$TARGET_IMPL" == "node" ]]; then
     # 仓库里的 OpenRC 服务默认指向 Go 二进制；Node 实现改为经 run.sh 启动
     sed -i 's|^command=.*|command="/opt/nexusgate-agent/run.sh"|' /etc/init.d/nexusgate-agent
   fi