在入口mart.dart中声明

MaterialApp下

debugShowCheckedModeBanner: false

代码如下

MaterialApp(
        title: 'App',
        theme: ThemeData(
          // This is the theme of your application.
          //
          // Try running your application with "flutter run". You'll see the
          // application has a blue toolbar. Then, without quitting the app, try
          // changing the primarySwatch below to Colors.green and then invoke
          // "hot reload" (press "r" in the console where you ran "flutter run",
          // or simply save your changes to "hot reload" in a Flutter IDE).
          // Notice that the counter didn't reset back to zero; the application
          // is not restarted.
          fontFamily: 'Nunito',
        ),
        debugShowCheckedModeBanner: false, // 去除flutter右上角的debug字眼
     
        body: new Login(),
      )
    )