As an emerging field, the online short-term rental in China appears with poor national policy and industry general regulations. All enterprises in this industry are constantly groping for sustainable strategy of legitimacy. Previous studies on the online short-term rental mainly focus on the positive influence, the business model, and policy and regulation. However, there is currently little research on how the online short-term rental enterprises develop ecosystem and legitimacy during different phases involved, which provides a good reference for other emerging organization in sharing economy.This study applied business ecosystem and legitimacy to analyze the development of a typical online short-term rental company via a longitudinal interpretive case study. A process model of how an online short-term rental company’s sub-ecosystems is inductively derived and elucidates the regulative challenges, normative challenges, and cognitive challenges in each phase. The findings of this case study provide a comprehensive and empirically supported framework and demonstrate a successful process model.