近年来，国有企业改革取得了重要成效，但仍有一些国有企业的现代企业制度还不健全，存在内部人控制、管理混乱、国有资产流失等问题，成为社会和舆论所关注的焦点。十八大以来，混合所有制改革成为深化国有企业改革的重要内容。 本文对混合所有制股权结构与国有企业代理成本的相关问题进行了研究。本文首先通过对国有企业改革历程的回顾，指出国有企业改革要突破的核心是所有者缺位，混合所有制是解决这一问题的重要途径；然后对混合所有制股权结构进行了定义，并分析了混合所有制股权结构存在的理论基础；在此基础上，本文选取2003年到2019年上市国企为样本，研究了混合所有制股权结构对国有企业代理成本的影响，及其影响渠道，混合所有制股权结构的经济效果分析，总的来说，从原因，影响，对策三方面对混合所有制进行了全方面的分析。 本文的主要研究结论及贡献是： （1）混合所有制股权结构与国有企业代理成本负相关，能提高国企平均资产周转率约2%，降低国企管理费用率约4.5%。竞争性行业的企业、央企、法治环境较好地区的企业，相对而言混合所有制股权结构降低代理成本的作用更加显著。本文通过分析国有企业形成混合所有制股权结构的原因，并经过PSM-DID回归分析后，基本结果依然显著。最后，通过使用工具变量，替换有关解释变量，增加控制变量等方法后实证结果依然显著。 （2）混合所有制股权结构通过减少政策负担，完善董事会监督机制，增强高管的业绩薪酬敏感性和CEO业绩离职敏感性，增加薪酬差距，这四个渠道起到降低国有企业代理成本的作用，也就是完善了公司治理结构。 （3）具有混合所有制股权结构的国企盈利能力更高，创新产出更多，生产效率更高。 本文为现实中的国有企业改革验证了新的实践思路，为公有制的实现形式提供了理论基础，丰富了有关民营化的文献，对于广泛的公司治理文献提供了新的分析方向，同时丰富了大股东治理方面的文献。

In recent years, China’s state-owned enterprises (SOEs) reform has made great progress, while some firms did not have a complete modern company mechanism, and there exists problems such as: chaotic management, insider control and state-owned asset loss, which have become the focus of society and public opinion. Since the 18th CPC National Congress, the reform of mixed ownership has become an important part of deepening the reform of state-owned enterprises. This paper mainly investigates some questions about mixed ownership structure and SOEs’ agency costs. Firstly, this paper reviews the history of state-owned enterprise reform and points out that the core of SOEs reform is solving the absence of firm owner, in which the mixed ownership structure plays an important role. Then it defines the mixed ownership structure, and analyzes the theoretical basis of the mixed ownership structure. On these bases, this paper selects A-share listed state-owned enterprises from 2003 to 2019 as a sample to study the impact of mixed ownership structure on the agency cost of state-owned enterprises, its influence channels, and the economic effects of mixed ownership structure. In general, this paper conducts a comprehensive analysis of mixed ownership structure from three aspects: causes, effects and advices. The main research conclusions and contributions of this paper are as follows: (1) The mixed ownership structure is negatively correlated with the agency cost of state-owned enterprises, which can improve the average asset turnover rate of state-owned enterprises by about 2% and reduce the average management expense rate of state-owned enterprises by about 4.5%. Relatively speaking, the role of mixed ownership structure in reducing agency costs is more significant in competitive industries, central government owned enterprises, and enterprises in areas with better legal environment. Through finding the reasons for the formation of mixed ownership structure in state-owned enterprises, and conducting PSM-DID regression analysis, the main results are still significant. The regression results are still significant after using instrumental variable method, replacing variables and adding control variables. (2) The mixed ownership structure reduces the agency costs and improves the SOEs’ corporate governance structure by reducing the policy burden, improving the supervision mechanism of the board of directors, enhancing the performance compensation sensitivity and performance resignation sensitivity of senior executives and CEOs, and increasing the salary gap. (3) The mixed ownership structure is positively correlated with the company's operating performance, the company's innovation output and the enterprise's production efficiency. This paper verifies new practical ideas for the reform of state-owned enterprises in reality, providing a theoretical basis for the realization form of public ownership, enriching the literature on privatization, providing a new analysis direction for a wide range of corporate governance literature, and enriches the literature on the governance of major shareholders.