Competition is the inherent requirement of market economy.The Anti-Monopoly Law and Anti-Monopoly Enforcement are the core contents and tools of competition policy,which are conducive to protecting,promoting and regulating market competition,and are an important guarantee for the market to play a decisive role in resource allocation.Based on the difference-in-differences method,this paper examines how the"three-in-one"reform of Anti-Monopoly Enforcement Agency in 2018 affects the company's equity financing.We find that after the Anti-Monopoly Enforcement Agency Reform,the equity financing for companies with high monopoly degree has decreased significantly compared with those with low monopoly degree.The mechanism test shows that the Anti-Monopoly Enforcement Agency Reform affects equity financing by changing the competitive environment and business environment of market players.The cross-sectional analysis finds that the restraining effect of Anti-Monopoly Enforcement Agency Reform on equity financing is greater in state-owned enterprises and large enterprises.Furthermore,we show that compared with equity financing,the Anti-Monopoly Enforcement Agency Reform has a more serious inhibiting effect on debt financing,and after the Anti-Monopoly Enforcement Agency Reform,the equity refinancing behavior of companies with high monopoly degree has been significantly restricted,and the cost of equity capital has increased significantly.The conclusion of this paper has certain enlightenment significance for optimizing the efficient and rational allocation of financial resources and promoting the high-quality development of enterprises from the perspective of competition regulation.