I have a question about shia and sunni shia are Muslims? And sunni can marry with shia?

This is really a question for your own iman.

Shia vs Sunni - Difference and Comparison | Diffen (http://www.diffen.com/difference/Shia_vs_Sunni)

What's the Difference Between Shia and Sunni Muslims? (http://islam.about.com/cs/divisions/f/shia_sunni.htm)

Please think twice before you ask something like this. Why wouldn't it be allowed to marry a shia woman who is also a muslim, when it is even allowed for a man to marry a christian woman or jewish woman?