Through corpus-based and theoretical analysis, it can be confirmed that the cleft construction ‘Shi…De’ has more restrictions than the focus construction with ‘Shi’. First, the cleft construction is used only for past events, whereas the focus construction can be used for past, present and future events. Second, in terms of information structure, the argument that follows the focus marker ‘Shi’ always functions as a unique focus in a cleft construction, while a focus construction with ‘Shi’ can have an argument-focus structure, a predicate-focus structure, or a sentence-focus structure. Third, an indefinite noun phrase cannot follow a verb in a cleft construction, but it can follow a verb in the focus construction with ‘Shi’. Fourth, there are restrictions on the situational types of verbs used in the cleft construction, but there are few restrictions on those of verbs in the focus construction with ‘Shi’. This study shows that the pragmatic functions of the cleft construction and the focus construction are totally different, and the view that the information structure of the two constructions is the same is not appropriate.