cd /etc/apt
cp sources.list sources.list.bak
vi sources.list

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

# 更新apt数据源
apt-get update

注：查看更多系统的国内镜像源 https://mirrors.tuna.tsinghua.edu.cn/help/debian/