This research robustly investigates and verifies the impact of science-technology intermediary (STI) on regional innovation for panel data covering 31 provinces in China from 2000 to 2019. Overall, we find that STI's effects on regional innovation are positive, no matter in the static or dynamic model, reflecting that more innovation-related entities may be motivated to plug into a STI-centered network due to increasingly positive externality, which in turn strengthens STI's innovation-enhancing effect over time. Giving consideration to both development and transaction costs in innovation activities, this study explores three mechanisms of the STI-innovation nexus. (1) STI reduces transaction cost, which then stimulates collaborations of innovation. (2) STI facilitates specialization in innovation-related resources' optimal redistribution, improving regional capacity to successfully convert existing elements into innovation outputs. (3) STI strengthens the capacity to absorb the knowledge spillover from neighboring provinces and foreign countries. All arguments herein are supported for the case of China.