sudo: pip: command not found in CentOS

I use CentOS and I installed pip to /usr/local/python-dir/bin/pip. I made a link to /usr/local/bin/pip. Then I executed sudo pip install xxx, it reported an error like this: sudo: pip: command not found I see $PATH is all right: /usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin However, I can only execute pip this way: sudo /usr/local/bin/pip install xxx How can I configure PATH or something