首先先备份源文件

使用vim可以参考[Linux宇宙]vim编辑器的使用说明 – www.hawkjgogogo.com

可以通过默认模式下输入:set mouse=r，愉快地使用右键复制粘贴进行以下操作：

阿里云源：

deb http://mirrors.aliyun.com/debian/ buster main contrib non-free
deb-src http://mirrors.aliyun.com/debian/ buster main contrib non-free

deb http://mirrors.aliyun.com/debian-security/ buster/updates main contrib non-free
deb-src http://mirrors.aliyun.com/debian-security/ buster/updates main contrib non-free

deb http://mirrors.aliyun.com/debian/ buster-updates main contrib non-free
deb-src http://mirrors.aliyun.com/debian/ buster-updates main contrib non-free

deb http://mirrors.aliyun.com/debian/ buster-backports main contrib non-free
deb-src http://mirrors.aliyun.com/debian/ buster-backports main contrib non-free

清华大学源：

deb https://mirrors.tuna.tsinghua.edu.cn/debian/ buster main contrib non-free
deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ buster main contrib non-free

deb https://mirrors.tuna.tsinghua.edu.cn/debian-security/ buster/updates main contrib non-free
deb-src https://mirrors.tuna.tsinghua.edu.cn/debian-security/ buster/updates main contrib non-free

deb https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-updates main contrib non-free
deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-updates main contrib non-free

deb https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-backports main contrib non-free
deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-backports main contrib non-free

保存并关闭文件。然后，运行以下命令更新软件包缓存：
sudo apt update
现在，您的Debian系统已经更换为国内源。使用国内源可以加快软件包的下载速度，并提供更稳定的连接。请注意，根据您所在地区和具体需求，选择适合您的合适源。