This paper studies the influence and mechanism of state-owned shareholders on human capital structure of private enterprises in Shanghai and Shenzhen A-share listed companies from 2011 to 2021. The research shows that state-owned shareholders can promote the upgrading of human capital structure in private enterprises; The mechanism analysis shows that improving the social status, strengthening the protection of employees’ rights and interests and enhancing the willingness of research and development are the mechanism of improving the human capital structure of state-owned shareholders. From the perspective of function path, the state-owned shareholders optimize the human capital structure of participating private enterprises by squeezing out the low education and production personnel; This effect is heterogeneous. Low government intervention and factor market development can positively adjust the effect of state-owned shareholders on the improvement of human capital structure. Economic outcome test shows that the positive influence of state-owned shareholders on human capital structure can not only “make the cake bigger” in business performance, but also play a role in “dividing the cake” in income distribution pattern. The conclusion not only enriches the literature on mixed ownership reform and human capital upgrading, but also provides reference for private enterprises to optimize the allocation of human resources by using state-owned capital.