尝试更换以下源：

阿里

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

清华大学

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

中国科技大学

deb https://mirrors.ustc.edu.cn/debianbuster main contrib non-free
deb https://mirrors.ustc.edu.cn/debianbuster-updates main contrib non-free
deb https://mirrors.ustc.edu.cn/debianbuster-backports main contrib non-free
deb https://mirrors.ustc.edu.cn/debian-security/ buster/updates main contribnon-free

SJTUG思源

deb https://mirror.sjtu.edu.cn/debianbuster main contrib non-free
deb https://mirror.sjtu.edu.cn/debianbuster-updates main contrib non-free
deb https://mirror.sjtu.edu.cn/debianbuster-backports main contrib non-free
deb https://mirror.sjtu.edu.cn/debian-security/ buster/updates main contribnon-free

浙江大学

deb https://mirrors.zju.edu.cn/debian/ buster main contrib non-free
# deb-src https://mirrors.zju.edu.cn/debian/ buster main contrib non-free
deb https://mirrors.zju.edu.cn/debian/ buster-updates main contrib non-free
# deb-src https://mirrors.zju.edu.cn/debian/ buster-updates main contrib non-free
deb https://mirrors.zju.edu.cn/debian/ buster-backports main contrib non-free
# deb-src https://mirrors.zju.edu.cn/debian/ buster-backports main contrib non-free
deb https://mirrors.zju.edu.cn/debian-security buster/updates main contrib non-free
#deb-src https://mirrors.zju.edu.cn/debian-security buster/updates main contrib non-free

以上镜像更新时总有报错，Debian更新失败，最后找到的debian.org解决问题,apt-get update成功。

以下默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释：

# deb http://snapshot.debian.org/archive/debian/20200607T000000Z buster main
deb http://deb.debian.org/debian buster main
# deb http://snapshot.debian.org/archive/debian-security/20200607T000000Z buster/updates main
deb http://security.debian.org/debian-security buster/updates main
# deb http://snapshot.debian.org/archive/debian/20200607T000000Z buster-updates main
deb http://deb.debian.org/debian buster-updates main