Reducing the proportion of State-owned Shares, as a method of Mixed Ownership Reform (MOR) in State-owned Enterprises (SOEs), is of great significance for realizing the preservation and appreciation of state-owned assets and improving the efficiency of state-owned shareholders'' shareholding. The data of China’s A-share manufacturing SOEs were selected from 2010 to 2019, from the perspective of two mechanisms of government subsidy and organizational complexity, based on the three-stage DEA model, and on the basis of corporate efficiency indicators after excluding environmental factors and random noise, construct a multi-period DID model to discuss the impact of the reduction of the proportion of state-owned shares on the Total Factor Productivity (TFP) of SOEs. The results show that a reduction in the proportion of state-owned shares can significantly increase the TFP of SOEs, and has a two-year lag period. Among them, reducing the level of government subsidies and optimizing the complexity of the organization will increase the TFP of enterprises. Further research finds that the TFP of SOEs in competitive industries and capital-intensive industries after the MOR is more obvious; high leverage risk SOEs, low ''principal-agent'' cost of SOEs, the TFP after the MOR is more obvious. Based on the perspective of mixed ownership reform, the research explores the impact of the reduction in the proportion of state-owned shares on the TFP of SOEs, and proposes corresponding policy recommendations for the direction of the next mixed ownership reform.