Property right protection is the core of ownership, and at the same time it is the key to success or failure of mixed ownership reform. The paper takes 238 mixed ownership enterprises listed on A shares in China in 2016 as the research sample, and uses the PSM method to select paired samples, constructs the econometric model of mixed ownership, internal control and property rights protection. The study found that mixed ownership enterprises did not significantly increase property protection level; There is an inverted U relationship between the mixed depth, the degree of the balance of shares and property protection level, namely the medium mixed depth and shares balance degree is more conducive to the protection of property rights. The property protection level of state-owned control enterprises is higher than that of non-state holding enterprises, while non-state controlling shareholders are more appropriate to balance shareholders. Good internal control helps to raise the level of property rights protection, and internal control has a significant positive moderating effect on the depth of mixed, shares balance degree and the protection of property rights. This paper enriches the research on the economic consequences of internal control, and provides relevant empirical evidence for the reform of state-owned enterprises' mixed ownership at the level of corporate governance.