Objective Mental health is a fundamental aspect of residents’ health. However, in the context of rapid urban development, the pace of life for urban residents has accelerated significantly, leading to the prevalence of unhealthy lifestyles such as prolonged sedentary behavior and sleep deprivation. Consequently, various mental health issues including mental illness have become increasingly prominent. Therefore, addressing this mental health crisis has not only emerged as an urgent global concern but also constituted a crucial component in the construction of a healthy city in China. Urban greenways are linear green spaces accessible to pedestrians and cyclists. They are developed along natural and artificial corridors, such as riverfronts and scenic zones, to deliver health benefits to surrounding residents. As an integral component of urban ecological environments, green spaces serve as a significant resource for improving the mental health of urban residents. However, rapid urbanization has resulted in a decline in both the quantity and quality of urban green space, leading to increasingly prominent environmental problems and threats to public health. Therefore, conducting an in-depth exploration into the influence mechanism of green spaces on residents’ mental health holds great theoretical and practical significance for formulating intervention measures aimed at improving residents’ mental health.

Methods This research initially purposes a hypothesis regarding the relationship between urban green space and residents’ mental health. Subsequently, a quasi-natural experiment is conducted by administering a questionnaire survey to residents in 52 communities surrounding the East Lake Greenway during the baseline period in April 2016 and the follow-up period April 2019. Descriptive statistical analysis and reliability analysis are then performed on the survey data using SPSS 25.0 and AMOS 25.0. Finally, with changes in physical activity, physical health and emotional status as mediating variables, the research constructs a structural equation model (SEM) to analyze the causal mechanism linking urban green space intervention with changes in residents’ mental health while identifying potential differences between male and female groups.

Results Greenway exposure may directly influence residents’ mental health in a significant manner, and may also indirectly influence mental health through two mediators, namely changes in physical health score and body mass index (BMI). However, greenway exposure does not indirectly enhance mental health by influencing emotional changes. Furthermore, there are gender-specific differences in the causal mechanisms between greenway exposure and mental health. In the female group, greenway exposure may directly influence the magnitude of change in mental health scores, whereas no significant direct relationship is observed between greenway exposure and changes in male’s mental health scores. Regarding indirect influence, greenway exposure influences the mental health of females through BMI changes, while the relationship between greenway exposure and men’s mental health is mediated by changes in physical activities with moderate-to-high intensity and physical health scores. This research reveals the intricate causal mechanism linking greenway exposure to changes in residents’ mental health, while also identifying gender-specific disparities in the health influences of green spaces. To further enhance the benefits offered by the East Lake Greenway for improving residents’ mental health, several measures can be implemented. Firstly, enhancing the accessibility of urban greenways is of crucial importance in promoting residents’ mental health. It is recommended to increase secondary entrances and exits of the greenway within residential areas characterized by high population density and extensive residential land surrounding the greenway. Additional measures include fostering mixed development of land around the greenway, establishing a well-equipped public transportation system, as well as creating a safe, convenient and continuous slow traffic system. Hence, the connectivity between greenway entrances and residential areas and the frequency of residents to visit the greenway can be improved, consequently indirectly amplifying the positive influence on their mental health. Secondly, urban greenways have the potential to enhance residents’ physical activity and overall physical health, thereby improving their mental health. This research proposes to improve the public service facilities of greenway and strategically allocate fitness activity venues and amenities within open spaces to help diversify physical activities among residents. This approach may greatly benefit residents’ physical health and help them maintain optimal BMI levels, ultimately contributing to indirect improvement of residents’ mental health. Thirdly, variations exist in the causal mechanisms underlying the influence of urban greenway exposure on the mental health of different gender groups. Consequently, it is imperative to carefully configure service facilities based on distinct characteristics pertaining to green space utilization among various groups. The research proposes that urban greenway planning and design should primarily focus on enhancing the continuity and safety of walking paths while also providing comfortable seating at appropriate intervals to cater to the requirements of females for walking activities and reducing BMI levels. For males, the research recommends optimizing greenways as physical activity venues to facilitate their engagement in moderate to vigorous physical activities and improve overall physical fitness, thereby promoting their mental health.

Conclusion This research provides a novel perspective on improving the quality of large-scale green infrastructure in densely populated urban areas, thereby contributing to the promotion of “Healthy China” and “Healthy City” through green space intervention for improving the mental health and well-being of urban residents. In future research, efforts will be made to optimize experimental design for objective measurement of residents’ health outcomes. Additionally, there will be a focus on investigating the causal mechanism underlying the influence of green space on mental health among different groups with diverse socioeconomic characteristics, as well as exploring the social equity related to the health effects of green space.