Legitimacy resources play a vital role in the survival and development of platform-based enterprises. However, in the current literature there is little systematic study on how to obtain legitimacy and what kind of legitimacy to obtain during the growth and development of platform-based enterprises. This study analyzes the growth and development of Didi as a case, and explores how different types of legitimacy resources needed for enterprise development can be obtained at different stages of platform-based enterprises to support their development. The study finds that in the process of growth and development of platform-based enterprises, different types of legitimacy resources are needed at different stages of the enterprise: the initial period requires cognitive legitimacy, and the period of shock stage needs normative legitimacy and regulative legitimacy is required in the period of stability. Institutional pressure is the dominant factor that determines legitimacy acquisition. Platform-based enterprises obtain legitimacy dynamically along the path of “being embedded, compliant and constructive” for the gradual realization of legitimacy.