[1] 首先备份/etc/yum.repos.d/CentOS-Base.repo
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
[2] 进入yum源配置文件所在文件夹
[root@localhost yum.repos.d]# cd /etc/yum.repos.d/
[3] 下载163的yum源配置文件，放入/etc/yum.repos.d/(操作前请做好相应备份)
[root@localhost yum.repos.d]# wget http://mirrors.163.com/.help/CentOS7-Base-163.repo
[4] 运行yum makecache生成缓存
[root@localhost yum.repos.d]# yum clean all
[root@localhost yum.repos.d]# yum makecache
[5] 更新系统
[root@localhost yum.repos.d]# yum -y update
原文：http://www.cnblogs.com/or2-/p/4600811.html