终端输入如下命令
nano /etc/apt/sources.list
然后把原来的都注释掉,粘贴下面源
deb http://mirrors.ustc.edu.cn/debian stretch main contrib non-free
deb http://mirrors.ustc.edu.cn/debian stretch-updates main contrib non-free
deb http://mirrors.ustc.edu.cn/debian stretch-backports main contrib non-free
deb http://mirrors.ustc.edu.cn/debian-security/ stretch/updates main contrib non-free
然后保存即可