Because the tar xvfz xampp-linux-1.6.6.tar.gz -C /opt doesn't work,  I split the whole process to 4 steps:

1, tar xvfz xampp-linux-1.6.6.tar.gz

2, mkdir /opt

3, mv /root/lampp /opt

4, /opt/lampp/lampp start

That’s ok. The xampp can work wonderfully.