Based on the policy background of “two-way mixing”in China’s mixed-ownership reform, this paper examines the internal mechanisms, action paths, and boundary conditions of the impact of state-owned capital participation on the human capital structure of private enterprises. The study finds that the impact of state-owned capital participation on the human capital structure of private enterprises presents an inverted U-shaped relationship. The internal mechanism of this impact lies in the interaction and dynamic balance between “fairness” and “efficiency” in employee management brought about by the participation of state-owned capital, and organizational management effectiveness and employee relationship quality as two critical action paths. Further analysis suggests that the coordination of development strategies prior to state-owned capital participation and the appointment of directors and supervisors afterward can both have positive moderating effects.