The core of the mixed ownership reform is to establish a modern enterprise system to achieve the separation of the ownership and management of the companies. Based on the existing theories, this article puts forward that during the reform of SOEs, ownership should also include the right to control; the separation of ownership and management should be demonstrated as a unity of opposites. lt also sorts out the multiple agency problems faced by SOEs after the mixed ownership reform, and finds that the mixed ownership reform can help to alleviate the conflicts among different stakeholders and reduce the agency costs. With the classic valuation model, it infers that mixed ownership reform is helpful for SOEs to maintain and increase their value. By analyzing relevant theories of capital structure, it concludes that the introduction manner and pace of non-public capital should match the investment efficiency and capital cost.