<p>As a global pioneer in green innovation, does China’s low-carbon policy system support the Porter Hypothesis by stimulating technological progress? While prior research has examined the individual effects of environmental policies, relatively little attention has been paid to the synergy between heterogeneous policy instruments. This study investigates the effects and mechanisms of command-and-control low-carbon policies (CLP) and market-based low-carbon policies (MLP), as well as their combined impact on green innovation, providing both theoretical refinement and empirical evidence. Using panel data from 282 Chinese cities, we employ a two-way fixed effects model and a battery of robustness tests. The empirical results demonstrate that both CLP and MLP significantly promote green innovation, and their combination generates a positive policy synergy that jointly incentivizes innovators’ activities. Mechanism analysis further reveals that the two policies and their interaction alleviate firms’ financing constraints and enhance industrial performance at the city level. Moreover, the heterogeneity analysis shows that MLP exerts a stronger effect in cities with higher fiscal pressure, lower state-owned asset shares, and lower dependence on high-energy-consuming industries, whereas CLP plays a more important role in cities with the opposite characteristics. Importantly, the synergistic effect of CLP and MLP is most pronounced in cities with higher fiscal pressure, larger state-owned asset shares, and greater reliance on high-energy-consuming industries. These findings enrich the understanding of low-carbon policy design and offer practical implications for emerging economies pursuing green transformation.</p>