This paper conduct a research on the impact of non-state-owned shareholder governance on the supplier structure of state-owned enterprises in the context of mixed ownership reform. The results show that the participation of non-state-owned shareholders in the high-level governance of state-owned enterprises can significantly reduce the dependence of state-owned enterprises on large suppliers, and thus play a positive role in the optimization of state-owned enterprises’ supplier structure. The results of the mechanism show that the participation of non-state-owned shareholders in governance can improve the market competitiveness of SOEs and ultimately reduce their dependence on large suppliers. Further research found that this governance effect is more pronounced in SOEs that are small in scale, low in growth, low in digital development, and controlled by local governments. The research shows that the participation of non-state-owned shareholders in the high-level governance of state-owned enterprises can exert a positive impact on the optimization of the supplier structure of state-owned enterprises.