The “bottleneck” technology in key areas is an important factor restricting the development of new quality productive forces in China. It is of great practical significance to explore how to promote micro-enterprises to break through key core technologies. As an important vehicle for local governments’ industrial investment, urban investment platforms have increasingly engaged in the cultivation of strategic emerging industries and the pursuit of breakthroughs in key core technologies through equity investment, emerging as a pivotal instrument for steering industrial upgrading. However, existing research mostly explores the economic consequences of urban investment platforms investing in listed companies from their own perspective, while whether and how such investment behavior facilitates investee enterprises’ breakthroughs in key core technologies remains to be empirically tested. In view of this, based on a sample of A-share listed companies from 2015 to 2022, this paper empirically finds that equity participation of urban investment platforms significantly promotes breakthroughs in key core technologies. Mechanism testing reveals that equity participation of urban investment platforms drives such breakthroughs primarily through two channels: government strategic guidance and innovative resource support. Heterogeneity analysis indicates that the promotion effect is more pronounced in regions with stronger basic research capacity, those with lower issuance of urban investment bonds, and enterprises with non-bailout intentions. Furthermore, tests for distinguishing platform business types indicate that equity participation of industrial and comprehensive types of urban investment platforms can be more conducive to promoting breakthroughs in key core technologies. Further research shows that urban investment platforms investing in listed companies also generate a positive innovation spillover effect by stimulating substantive innovation activities among upstream and downstream enterprises through industrial chain synergy. The study also finds that equity participation of urban investment platforms exerts no significant positive effect on corporate strategic innovation in non-key and non-core technology fields. This paper offers important policy implications for refining the government’s industrial investment mechanisms and advancing the development of new quality productive forces.