Abstract: Against the backdrop of deepening new technological and industrial revolutions, technological innovation serves as the core driver in building a modern industrial system and promoting high-quality economic development. As the "backbone" and "ballast stone" of the national economy, how state-owned enterprises can lead and drive technological innovation among private enterprises and their upstream and downstream counterparts is not only a crucial exploration in advancing high-quality collaborative development between SOEs and private enterprises but also a key issue in cultivating the core competitiveness of a modern industrial system. Based on this, this article uses data from private enterprises listed on the Shanghai and Shenzhen A-shares from 2009 to 2023, as well as their top five suppliers and customers, as samples to empirically test the spillover effects of industrial chain innovation of state-owned capital participation in private enterprises. The conclusions are as follows: Firstly, state-owned capital participation significantly promotes innovation in both upstream and downstream enterprises of the private enterprise industry chain. Secondly, the mechanism test finds that the innovation spillover effects generated by state-owned capital participation mainly play a role through two levels: the industrial chain and the enterprise. At the level of the industrial chain, by stabilizing the supply-demand relationship and optimizing supply-demand matching, we can break through the "external threat" dilemma of enterprises; at the enterprise level, by alleviating financing constraints and promoting technology spillover, the "internal concerns" of enterprises can be solved, thereby promoting innovation among upstream and downstream enterprises in the industrial chain of private enterprises that are invested in. Thirdly, the heterogeneity test finds that when the upstream and downstream industries are highly competitive and the geographical distance from the privately-owned enterprises being invested is shorter, the innovation-promoting effect of state capital participation is stronger. Additionally, the innovation spillover effect generated by local state shareholders is more pronounced. Fourthly, the expansion test finds that after distinguishing the types of innovation spillover, industry characteristics, and behavioral characteristics, the innovation spillover effects of state-owned capital participation in private enterprises are mainly reflected in downstream enterprise pull and industry drive, and the technological innovation of upstream and downstream enterprises is active learning rather than passive imitation behavior. Based on the above findings, the following recommendations are put forward: First, persist in deepening the reform of mixed ownership, promote mutual empowerment between state-owned enterprises and private enterprises in the construction of a modern industrial system, and work together to promote high-quality economic and social development. Secondly, from the industry chain and enterprises to make concerted efforts to cast the endogenous foundation of the innovation spillover effect of the industry chain of state-owned capital participation in the endogenous foundation. Thirdly, tailoring measures to local conditions and enterprises, enhancing the precise "drip irrigation" role of state-owned capital participation. The research conclusion provides reference for strengthening the leading efficiency of state-owned capital support and promoting the collaborative construction of a modern industrial system between state-owned enterprises and private enterprises.

Key words: state capital participation, private enterprise innovation, mixed ownership reform, industry chain spillover effect