Abstract: Sentences like “Insistence, that is (na shi) something quite difficult” have the emphatic feature. It is a kind of cleft sentences formally and it contains a focus functionally. The word “na” refers to an abstract category. The structure “Na shi ” approaches to a set expression. Such structure is similar to the English cleft mode “it is ”. Nonetheless, it can mark the contrastive focus and express the natural one. Both the structure “na shi” and the common “shi” construction are the focus expressions. They are restrained by the Chinese structural features and hence are not used frequently.