网络映像使用此代码：

new CircleAvatar(
                      radius: 60.0,
                      backgroundColor: const Color(0xFF778899),
                      backgroundImage: NetworkImage("Your Photo Url"), // for Network image

                    ),

将此用于资产图像：

new CircleAvatar(
                      radius: 60.0,
                      backgroundColor: const Color(0xFF778899),
                      child: new Image.asset(
                        'images/profile.png',
                      ), //For Image Asset

                    ),

如果你使用backgroundImage作为CircleAvatar的图像提供者，那么改变radius属性实际上没有任何效果。从源代码circle_avatar.dart可以观察到图像被渲染为BoxFit。cover DecorationImage(image: backgroundImage, fit: BoxFit.cover)-在user_accounts_drawer_header.dart中currentAccountPicture被硬编码为72.0像素的SizedBox，所以图像的尺寸总是72.0px。
https://github.com/flutter/flutter/blob/master/packages/flutter/lib/src/material/user_accounts_drawer_header.dart#L57
https://github.com/flutter/flutter/blob/master/packages/flutter/lib/src/material/circle_avatar.dart#L203
希望Flutter团队在未来能在这方面增加一些控制水平。
不是答案，只是更多的信息，希望能帮助别人。

试试这个：

import 'package:flutter/material.dart';

class AppDrawer extends StatefulWidget {
  @override
  _AppDrawerState createState() => new _AppDrawerState();
}

class _AppDrawerState extends State<AppDrawer> {
  @override
  Widget build(BuildContext context) {
    return new Drawer(
      child: Center(
        child: Column(
          children: <Widget>[
            new UserAccountsDrawerHeader(
              decoration: BoxDecoration(color: Colors.white),
              currentAccountPicture: new CircleAvatar(
                radius: 50.0,
                backgroundColor: const Color(0xFF778899),
                backgroundImage:
                    NetworkImage("http://tineye.com/images/widgets/mona.jpg"),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

这是输出的屏幕截图：

将你的图片 Package 在CircleAvatar小工具中，它就是为了这个目的而设计的。

您将边距放在图像的容器内，而您必须使用UserAccountDrawerHeader的margin参数，这就是为什么您的图像变成椭圆形：

UserAccountsDrawerHeader(
          decoration: BoxDecoration(color: Colors.white),
            margin: EdgeInsets.only(bottom: 40.0),                                            
          currentAccountPicture: Container(  
            decoration: BoxDecoration(
                shape: BoxShape.circle,
                image: DecorationImage(
                    fit: BoxFit.fill,
                    image:
                        NetworkImage("https://via.placeholder.com/150"))),
          ),
          accountName: new Container(
              child: Text(
            'Name',
            style: TextStyle(color: Colors.black),
          )),
          accountEmail: new Container(
              child: Text(
            'Email',
            style: TextStyle(color: Colors.black),
          )),
        ),

您可以创建自己的标题：

DrawerHeader(
              decoration: BoxDecoration(
                color: Colors.blue
              ),
              child: ListView(
                children: [
                  return ClipRRect(
                    borderRadius: BorderRadius.circular(8.0),
                    child: Image.asset('images/myImage.jpg'),
                  ),
                  //These can go here or below the header with the same background color
                  Text("user name"),//customize this text
                  Text("useremail@example.com"),
                  //...additional header items here 
                ],
              )),

**我找到了解决办法！**至少这对我有效

import 'package:flutter/material.dart';

    class HomePage extends StatelessWidget {
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          // Side menu
          drawer: new Drawer(
            child: GestureDetector(
              onTap: () {},
              child: ListView(
                children: <Widget>[
                  new UserAccountsDrawerHeader(
                    accountName: new Text('Hymn +'),
                    accountEmail: new Text('johndoe@gmail.com'),
                    currentAccountPicture: new CircleAvatar(
                      backgroundImage: new NetworkImage(
                          'https://miro.medium.com/max/1400/1*uC0kYhn8zRx8Cfd0v0cYQg.jpeg'),
                    ),
                  ),
                ],
              ),
            ),
          ),
        );
      }
    }

这对我很有效：

DrawerHeader(
              decoration: BoxDecoration(color: Colors.blue),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  /*CircleAvatar(
                    radius: 50.0,
                    backgroundColor: const Color(0xFF778899),
                    child: new Image.asset('assets/images/profile_image.png'), //For Image Asset
                  ),*/
                  Container(
                    height: 110,
                    child: ClipRRect(
                      borderRadius: BorderRadius.circular(100.0),
                      child: Image.asset('assets/images/profile_image.png'),
                    ),
                  ),
                  //These can go here or below the header with the same background color
                  //Divider(height: 1.0, thickness: 1.0, color: Colors.black),
                  SizedBox(height: 9.0),
                  Text("user name"),
                  //...additional header items here
                ],
              ),
          ),