The Mixed Ownership Reform (MOR) seeks to establish a tripartite equilibrium among state shareholders, nonstate shareholders, and employee shareholders, achieving incentive compatibility among national interests, corporate objectives, and individual benefits. Grounded in Chinas MOR institutional context, this study examines employee stock ownership plans (ESOPs) governance effects on corporate internal control quality, transcending traditional “capital hybridity” research paradigms to establish a “human capital property rights actualization governance mechanism restructuring” analytical framework. Key findings demonstrate that ESOPs enhance internal control quality through residual claim sharing and risk cobearing mechanisms, yet exhibit an inverted Ushaped nonlinear effect: marginal benefits decline when employee participation approaches 50%, inducing collective action dilemmas. Heterogeneity analysis reveals amplified governance effects in nonexecutiveled schemes, leveraged financing models, and extended lock up periods. Post lock up short-term arbitrage incentives, however, provoke market value management behaviors that degrade control quality. These findings advance research on the “third pathway” governance effects within MOR, offering theoretical and practical guidance for optimizing governance structures in diversified ownership enterprises and achieving statecivilian collaborative development under China’s deepened factor marketization reforms.