Abstract: The entrepreneurship of Internet platform enterprises always from existing institutional field to new institutional field. They are often caught in a dilemma of institutional pressure in old field and institutional vacant in new field. Existing research lacks of deeply analysis of this strategy. This paper takes the case of online car-hailing enterprises which expand from taxi service field to express or premier field, analyzes the internal logic of institutional entrepreneurial behavior. The results show that: (1) The institutional pressure and institutional vacant in old and new institutional field make the goal of institutional work different. Old field emphasizes legitimacy acquisition by maintain institution, new field emphasizes legitimacy construction by create institution. (2) In old institutional field(taxi service), platform enterprises focus on supply-side to rapid and large-scale development based on existing supply-side users, then attract the demand-side users. It belongs to institutional entrepreneurship by maintain institution. In new institutional field(express or premier), platform enterprises explore the diversified needs of existing demand-side users, to create a diversified market and lock demand-side. (3)When platform enterprises reach the "cold start" of old institutional field, they should transfer from maintain institution to create institution. Once they enter new institutional field, the "tipping point" should be used as the goal, thus becoming the oligarch of the subdivision market. This paper analyzes the institutional entrepreneurial behavior of platform enterprises, combines the characteristics of platform reveals its internal mechanism, and provides a new idea for the application of institutional theory in the context of Internet platform.