Different from the conscious cash dividend behavior of the company, the mandatory dividend policy can not only correct the dividend behavior of the company, but also arouse the negative resistance of the executives. Therefore, it is difficult to predict whether it can effectively reduce the agency cost of the company. In this regard, this paper uses mixed strategy and complete information static game to explain the mechanism of mandatory dividend policy affecting agency cost, and takes the mandatory dividend policy introduced in 2011 as a quasi-natural experiment to test whether mandatory dividend policy can reduce the agency cost of listed companies. Empirical research finds that mandatory dividend policy significantly inhibits the agency cost of enterprises. Heterogeneity test shows that mandatory dividend-sharing policy has a better effect on reducing agency costs for companies listed on the motherboard and companies with normal dividends, but it has no significant effect on restraining agency costs for companies with micro-dividends and small and medium-sized boards. This study supports the dividend agency cost theory and provides empirical evidence for capital market to further improve dividend policy and protect minority shareholders.