Abstract: Cultivating state-owned enterprise groups with core competitiveness is a key task for comprehensively deepening the reform of state-owned enterprises in the new era, and is crucial to the high-quality development of the national economy. Taking non-state shareholders’ governance as the starting point, the impact of mixed ownership reform on structural efficiency of state-owned enterprise groups was investigated. It is found that non-state shareholders’ governance can improve the focus on the main business, ease government intervention, and improve the incentive mechanism for senior executives, thereby reducing the number of inefficient legal entities and improving the structural efficiency of state-owned enterprise groups. Further research shows that the above effect is more obvious after the State-owned Assets Supervision and Administration Commission of the State Council proposed “reducing the number of legal entities” in 2016, and is more prominent in state-owned enterprise groups with central control and high levels of market segmentation. Finally, under the governance of non-state shareholders, the optimization of structural efficiency of state-owned enterprise groups can better achieve digital transformation and the preservation and appreciation of state-owned assets.