Hi, thanks for your replies,
The OS type selected correctly from settings. We have a OL6.3 template, so whenever we want to have a new virtual machine we deploy from that template.
I compared the issue VM's settings with others that were deployed from same template, no abnormal appeared.
Also the issue VM has running vmware tool. I am don't use 5.5u2 web client yet, but I am wondering about that strange issue.