Amidst a backdrop of decelerating economic growth, China confronts mounting environmental challenges, including air pollution, water scarcity, and escalating carbon emissions. In this context, enhancing the urban ecological carrying capacity (UECC)– defined as the ability to sustain human activities without compromising environmental quality – emerges as a pivotal concern. To address these issues, the Chinese government has instituted the “Low Carbon Pilot Cities policy” initiative (LCPP), aiming to foster sustainable urban development by encouraging cities to adopt measures that reduce carbon emissions and enhance energy efficiency. This paper treats the policy as an exogenous quasi-natural experiment, employing a spatial double-difference methodology to assess its impact on the ecological carrying capacity of 281 Chinese cities from 2006 to 2021. Utilizing the pressure-state-response (PSR) model, this study constructs and evaluates their ecological carrying capacity. The findings reveal that: firstly, the low-carbon pilot policies significantly augment urban ecological carrying capacities; secondly, the policy's effects exhibit regional variability; thirdly, these policies bolster ecological carrying capacity through innovation-driven and energy structure optimization mechanisms; and fourthly, a further spatial spillover analysis indicates that the policy implementation adversely affects the ecological carrying capacity of adjacent cities. Consequently, this study offers empirical evidence and policy insights to assist countries in judiciously implementing environmental policies to achieve sustainable development objectives.