This study investigates the impact mechanism of the government's strategic leadership (SL) and environmental optimisation (EO) on the improvement of regional innovation performance (RIP) under the effects of the regional innovation system coupling synergy degree (RISCSD). Based on the nonlinear threshold regression model, the coupling synergy model and entropy value method, the threshold regression analysis is conducted by calculating the RISCSD. The results indicate that: under the effect of the RISCSD, the SL, EO, and RIP have distinct single and double threshold effects. With the improvement of RISCSD, the influence of SL on RIP has changed from inhibition to promotion; while the promotion effect of EO on RIP shows an upward trend at first, and then slightly weakening. This paper provides relevant policy suggestions for local public administrations to enhance RIP. [ABSTRACT FROM AUTHOR]