找到node_modules/angular-cli/lib/config/schema.json
default值就是默認(rèn)的端口

"serve": {
    "description": "Properties to be passed to the serve command",
    "type": "object",
    "properties": {
      "port": {
        "description": "The port the application will be served on",
        "type": "number",
        "default": 4200
      },
      "host": {
        "description": "The host the application will be served on",
        "type": "string",
        "default": "localhost"
      }
    }
  }
}

也可以通過命令行方式修改，如：

ng serve --port 4201