备份
mv /etc/apt/sources.list /etc/apt/sources.list.bak
修改文件
nano /etc/apt/sources.list
复制以下代码，保存

debian10的163

deb http://mirrors.163.com/debian/ buster main non-free contrib
deb http://mirrors.163.com/debian/ buster-updates main non-free contrib
deb http://mirrors.163.com/debian/ buster-backports main non-free contrib
deb-src http://mirrors.163.com/debian/ buster main non-free contrib
deb-src http://mirrors.163.com/debian/ buster-updates main non-free contrib
deb-src http://mirrors.163.com/debian/ buster-backports main non-free contrib
deb http://mirrors.163.com/debian-security/ buster/updates main non-free contrib
deb-src http://mirrors.163.com/debian-security/ buster/updates main non-free contrib
debian10的阿里云源

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

apt-get update
别的debian10源参考：https://cloud.tencent.com/developer/article/1590080