centos7.3用yum 报错Error importing repomd.xml for base: Damaged repomd.xml file

[root@localhost ~]# yum install gcc
Loaded plugins: fastestmirror
base | 4.0 kB 00:00:00
http://mirrors.163.com/centos/7/os/x86_64/repodata/repomd.xml: [Errno -1] Error importing repomd.xml for base: Damaged repomd.xml file
Trying other mirror.

One of the configured repositories failed (CentOS-7 -Base),
and yum doesn't have enough cached data to continue. At this point the only
safe thing yum can do is fail. There are a few ways to work "fix" this:

 1. Contact the upstream for the repository and get them to fix the problem.

 2. Reconfigure the baseurl/etc. for the repository, to point to a working
    upstream. This is most often useful if you are using a newer
    distribution release than is supported by the repository (and the
    packages for the previous distribution release still work).

 3. Run the command with the repository temporarily disabled
        yum --disablerepo=base ...

 4. Disable the repository permanently, so yum won't use it by default. Yum
    will then just ignore the repository until you permanently enable it
    again or use --enablerepo for temporary usage:

        yum-config-manager --disable base
    or
        subscription-manager repos --disable=base

 5. Configure the failing repository to be skipped, if it is unavailable.
    Note that yum will try to contact the repo. when it runs most commands,
    so will have to try and fail each time (and thus. yum will be be much
    slower). If it is a very temporary problem though, this is often a nice
    compromise:

        yum-config-manager --save --setopt=base.skip_if_unavailable=true

failure: repodata/repomd.xml from base: [Errno 256] No more mirrors to try.
http://mirrors.163.com/centos/7/os/x86_64/repodata/repomd.xml: [Errno -1] Error importing repomd.xml for base: Damaged repomd.xml file

上网找了各种方案都无法解决。为什么？
刚装机就报错，后来换成163的yum源,也是同样的报错。运行yum makecache也是同样的报错。