Abstract:With environmental pollution, climate change and resource scarcity being serious global issues, green entrepreneurship is increasingly seen as an approach to simultaneously address economic performance, environmental impact and social responsibility. As green entrepreneurship needs to consider both venture performance and social responsibility, it will be subject to legitimacy constraints at the system level. Whether these legitimacy constraints are favorable to green enterprise is not yet clear from current research. Especially for transition economies, the problem of whether proactive green enterprises facing legitimacy constraints under institutional uncertainty can achieve green performance requires further study. Thus, a theoretical model to determine the relationship between green proactiveness orientation (GPO), green performance, legitimacy, and transitional economics was proposed. Based on the data from 235 new Chinese green firms, the empirical results suggest that green startups launch with a green proactiveness orientation, which enables them to acquire a green performance advantage over their competitors. Improvements in green performance is also shown to be driven by the pressure from institutional legitimacy. Better green performance can be easily achieved if green startups have a higher level of legitimacy. However, against the background of transitional economies, the increase in institutional uncertainty will damage the promotion of political legitimacy and make the enterprises that are subject to political legitimacy constraints lose their green performance. Currently, political legitimacy is no longer an impetus. However, the increase in institutional uncertainty will strengthen the promotion of commercial legitimacy and cause green-oriented startups to pursue more commercial interests. Thus, to a certain extent, it will lead to market uncertainty. The conclusion of this study not only provides guidance for startups in different industries to develop green actions under the pressure of institutional constraints but also warns governments to improve policies and regulations quickly under different situations of institutional uncertainty.