The design of SO/SU/SF is very clean and easy to use, I want to have a similar one to host the Q/A service in my local company, is it open source? or does stack overflow service inc. have the Q/A hosting service?
['https://meta.superuser.com/questions/1179', 'https://meta.superuser.com', 'https://meta.superuser.com/users/19926/']
I'm sorry to say that no, you can't self host. And it is not open source.

But there are open source clones exist. One of the example is [cnprog](http://cnprog.com/). You can access the source [here](http://code.google.com/p/cnprog/) and [here](http://github.com/cnprog/CNPROG). 

After you have the source, you can do anything you want.
Check out [Area 51](http://area51.stackexchange.com/).