This paper investigates shi in Mandarin wh questions under the Generative Grammar, and proposes that the properties of shi should play two ways, one of which is copular verb, and the other is focus marker. Meanwhile, Mandarin wh questions should be divided into two types which be defined I and Ⅱtypes. The focus marker shi stays in the head of Focus Projection Position (FocP), and it subject moves to the specifier of FocP since the Extended Projection Principle. As focus constituent, the whphrase stays in situ and adjunct the specifier of FocP in logic form.