Background <p>Differences in physical activity levels partly reflect structural inequalities in access to health opportunities. According to the socio-ecological model theory, physical activity is influenced by multiple factors across individual characteristics, interpersonal relationships, community environments, and policy systems. Among these, the spatial distribution of fitness facilities, as a key component of urban planning, potential to reshape the allocation of community level and thus offers a novel pathway to alleviate health inequities. In recent years, the Chinese government has actively promoted the development of <i>the 15-minute fitness circle</i>, aiming to enhance residents’ access to exercise by optimizing the equitable allocation of community fitness resources.</p> Methods <p>This study utilizes data from the 2021 China General Social Survey (CGSS) to construct an analytical framework encompassing residents’ perceived accessibility to <i>the 15-minute fitness circle</i>, self-reported physical activity, and informal social support—including Relative support, friend support, and neighbor support. First, we examine the direct effect of residents’ perceived accessibility to <i>the 15-minute fitness circle</i> on their self-reported physical activity. Subsequently, we further analyze the mediating role of informal social support in this process.</p> Results <p>The results of this study indicate that: (1) residents’ perceived accessibility to <i>the 15-minute fitness circle</i> has a significant positive effect on public physical activity; (2) among the three dimensions of informal social support, support from relative, friend, and neighbor all show significant positive associations with physical activity. However, after controlling for support from relative and friend, the independent predictive effect of neighbor support on physical activity is no longer statistically significant; (3) informal social support partially mediates the relationship between perceived accessibility to <i>the 15-minute fitness circle</i> and physical activity. These findings highlight the practical significance of the public’s perceived accessibility to <i>the 15-minute fitness circle</i> in promoting physical activity among the public and provide strong empirical support for the implementation of this policy by the Chinese government.</p> Conclusions <p>From the perspective of health equity, this study reveals the potential pathway through which the synergy between residents’ perceived accessibility to urban fitness facility planning and informal social support may promote public physical activity. The findings provide empirical evidence that subjective perceptions of community fitness resources, together with informal social support, are associated with physical activity. These results offer valuable insights and potential policy references for developing countries in promoting equitable fitness infrastructure and advancing national health strategies.</p> Clinical trial number <p>Not applicable.</p>