中国经济已由高速增长转向高质量发展阶段，以创新驱动的高技术行业国企在高质量发展中发挥着重要作用。基于不同类型股东持股比例构建混合所有制改革变量，采用多时点DID检验混合所有制改革对国有企业创新投入的影响。结果发现：相比于非深度混改，深度混改能够提升高技术行业国企创新投入水平。采用倾向得分匹配法和交叠DID等方法进行稳健性检验后，该结果仍成立。在此基础上，研究发现，东部地区国企和高市场化地区国企混改的创新投入效应更加显著。机制检验结果显示，深度混合所有制改革可以通过强化监督和缓解代理问题提升企业创新投入水平。新一轮国企改革需要注重混改深度，充分发挥非国有股东的治理优势，激发高技术行业国企创新动力。

Over the past 40 years of reform and opening up, the mixed ownership reform of state-owned enterprises (SOEs) has complemented the reform of state-owned enterprises and the development process of private enterprises, made positive progress and remarkable achievements in the scale, scope, mode and speed of mixed reform, and also made great breakthroughs in institutional integration and mechanism construction. With the development of productivity and social changes, new problems have inevitably appeared in the practice of state-owned enterprise reform, and the mixed reform still needs to be further promoted, and how to develop a higher level of mixed reform is still worthy of further study. Mixed-ownership reform is not a one-way road for SOEs to accelerate their development, but a two-way rush between SOEs and private enterprises. The advantages of private enterprises in terms of market mechanism, efficiency and scientific and technological innovation are organically integrated with the capital, resources, technology and management advantages of SOEs, and the mixed-ownership reform enterprises burst out with vigor and strong development momentum. The complementary advantages of state-owned capital and private capital have effectively enhanced the superimposed value of their advantages in the mixed-ownership reform. When SOEs choose to carry out mixed ownership reform in what proportion and in what way, they should first clarify their own development demands, combine the characteristics of non-state-owned capital, and skillfully combine them to achieve a win-win situation.
Most of the existing literature on mixed reform and innovation focuses on the impact of changes in ownership structure on innovation. However, the mixed reform is not a simple diversification of equity, but the introduction of non-state capital with a high shareholding ratio and giving play to the governance role of non-state-owned shareholders. Previous studies on the mixed-ownership reform and innovation investment of SOEs?have mainly focused on the impact of changes in shareholding structure on innovation investment, but the proportion of shares held by non-state-owned shareholders introduced by the mixed-ownership reform to promote innovation investment has been seldom considered. In addition, the mechanism through which the deep mixed-ownership reform of SOEs will increase the innovation investment of SOEs in high-tech industries, and the differences in the role of mixed-ownership reform of SOEs in different regions on innovation investment are all worthy of in-depth exploration.
Using the data of listed SOEs in the A-share high-tech industry from 2010 to 2019, this paper adopts a multi-point DID to test the effect of mixed ownership reform on the innovation input of SOEs in China. Empirical results show that, compared with unmixed and deep mixed reform, it can promote the innovation investment level of SOEs in high-tech industries. The results hold valid after a series of robustness tests, such as predisposition score matching and overlapping DID. On this basis, it is found that the mixed innovation effect of SOEs is more obvious in the eastern region and the highly market-oriented region. The mechanism test confirms that by strengthening supervision and mitigating agency problems, the deep mixed-ownership reform can promote the innovation input of SOEs in high-tech industries. Therefore, more attention should be paid to the depth of substantive reform rather than form in the new round of SOE reform.
Compared with previous studies, this paper has made breakthroughs in three aspects. First, it carefully arranges the shareholding ratio of non-state-owned shareholders among the top ten shareholders of enterprises, divides the mixed reform into non-deep and deep mixed reform, and studies the impact of mixed reform on innovation investment by category, enriching the related research on mixed reform. Second, combined with the multi-stage DID model and multiple robustness tests, it analyzes the influence of the mixed reform of SOEs in the high-tech industry on the enterprise's innovation investment, and expands the boundaries of previous research. Thirdly, this paper not only pays attention to the impact of the internal deep mixed reform on innovation investment but also studies the impact of regional and marketization degree on the depth mixed reform of SOEs from the external environment of enterprises, which broadens the research ideas of the mixed reform of SOEs.