你把更新源换一下，然后重新试一下，换成国内阿里或者其它的。

命令行:先备份sudo /etc/apt/sources.list /etc/apt/sources.list.bak
然后编辑 sudo gedit /etc/apt/sources.list
把以下内容放进去替换掉原来的源

deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse ##测试版源 deb http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse # 源码 deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse ##测试版源 deb-src http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse # Canonical 合作伙伴和附加 deb http://archive.canonical.com/ubuntu/ xenial partner deb http://extras.ubuntu.com/ubuntu/ xenial main

save保存
命令行:sudo apt-get update
sudo apt-get upgrade
sudo apt-get install python3-tk