It is of theoretical and practical significance to study the impact of mixed-ownership reform, the core measure of stateowned enterprise (SOE) reform, on the green innovation of SOEs. Using the data of SOEs listed in the China A-share stock market from 2010 to 2019, this study empirically tested the impact, mechanisms, and heterogeneous impact of mixed-ownership reform on the green innovation of SOEs through a Propensity Score Matching+Difference-in-Differences (PSM-DID) model based on the shareholding ratio of non-state-owned shareholders among the top ten shareholders of state-owned enterprises. On this basis, this paper further explored the spillover effect of mixed-ownership reform on the green innovation of SOEs. The results showed that: ① Mixed-ownership reform could effectively promote the green innovation of SOEs. After using the placebo test and instrumental variable method to alleviate the endogenous problem and replacing the matching basis for the robustness test, the conclusion was still valid. ② The mechanism test showed that the improvement of corporate governance level and the knowledge spillover effect were important channels for mixed ownership reform to promote the green innovation of SOEs. The profit-seeking nature of non-state-owned shareholders might have a dampening effect on the green innovation of SOEs in mixed-ownership reform. ③ The heterogeneity analysis of industry characteristics showed that in competitive industries and environmental protection industries, mixed-ownership reform had a more obvious impact on promoting the green innovation of SOEs. ④ Although the mixed-ownership reform promoted the green innovation of SOEs, it was not the higher the better in terms of the proportion of non-state-owned shareholders. When non-state-owned shareholders accounted for 15% to 30%, the promotion effect on the green innovation of SOEs was most obvious. ⑤ The mixed-ownership reform had a spillover effect on the green innovation of unreformed SOEs, effectively promoting the substantive green innovation of these SOEs in the same industry. Therefore, the study proposes that the important role of mixed-ownership reform in green development should be fully recognized and the mixed-ownership reform of SOEs should be further promoted. We should promote the formation of a mutually balanced equity structure and rationally allocate the proportion of non-state-owned capital. At the same time, we should avoid the ‘one-size-fits-all’ mixed-ownership reform and adhere to the classification and stratification of orderly progress. [ABSTRACT FROM AUTHOR]