With urban development and economic growth, the decline in the quality and scale of blue-green spaces, coupled with the increasing demand for public health, necessitates enhancements in the quality of blue-green space that suffi ciently address the needs of diverse socio-economic groups to optimize health benefi ts. Nonetheless, extant research has predominantly focused on the health eff ects of exposure and access to individual blue or green spaces, whereas relatively little emphasis has been placed on the health impacts of blue-green space improvements, particularly regarding distance effects and differential impacts across population subgroups. This study investigates the parks and water systems in Beijing that experienced quality enhancements between 2020 and 2022. Utilizing survey data from the “Beijing Urban and Rural Residents’ Life and Community Governance” studies conducted in 2020 and 2022, we analyzed a sample comprising 1 270 middle-aged and elderly people (aged 45 and above). Using a diff erence-in-diff erences (DID) approach, we investigated the relationship between improvements in blue-green space and mental health, and assessed the spatial heterogeneity of these eff ects on self-rated health, depression level, frequency of negative emotions, psychological resilience, and life positivity. The results indicate that improvements to blue-green spaces do not have a signifi cant positive impact on the psychological health of middle-aged people. However, for the elderly, improvements in blue-green spaces signifi cantly enhance psychological health, with notable spatial heterogeneity in these eff ects. Specifi cally, within a 1.6 km radius, blue-green space improvements signifi cantly improve older adults’ self-reported health; within a 1.2 km radius, they significantly alleviate depression levels. Although blue-green space improvements did not signifi cantly reduce negative emotions, they signifi - cantly promoted psychological resilience for older adults within a 1.2 km radius, with no signifi cant eff ects within 0.8 km or beyond 1.6 km. Furthermore, improvements to blue-green spaces signifi cantly enhance life satisfaction among older adults, and these positive eff ects increase with distance. The fi ndings reveal the mechanisms by which improvements in blue-green spaces aff ect health across diff erent age groups, particularly the diff erential eff ects based on spatial distance, providing theoretical and empirical support for future urban green space planning and social welfare policies.