Abstract: Promoting urban green development is an inevitable choice for China's current high-quality development. Based on panel data from 284 prefecture-level cities in China between 2003 and 2021, this study examines the impact of jointly implementing low-carbon city pilot policies and innovative city pilot policies on urban green development efficiency. The findings reveal that both the separate and combined implementation of these policies significantly enhance urban green development efficiency, with the combined effect surpassing that of individual implementations. The optimal policy sequence is to first implement low-carbon city pilot policies followed by innovative city pilot policies. The synergistic effect of these policies is more pronounced in cities with high economic agglomeration, vibrant entrepreneurial activity, and longer policy implementation durations. Effective transmission mechanisms for realizing policy synergies include reducing energy consumption per unit output, developing green technologies, and facilitating industrial transformation and upgrading. Currently, measures such as constructing a policy coordination system, focusing on key pilot cities, and targeting critical mechanisms should be adopted to actively leverage the role of low-carbon and innovative city pilot policies in promoting urban green development efficiency, thereby continuously advancing high-quality economic and social development in China.

Key words: green development efficiency, low-carbon cities, innovative cities, policy superposition, high-quality development