Previous studies have shown that natural environments and leisure activities can reduce depression and increase well-being. Urban parks are important for the psychological well-being of middle-aged and older adults. However, it remains unknown whether the relationship between environmental perceptions, leisure activity, and well-being is affected by the quality of park environments. This study uses a cross-level framework to examine the effects of urban park quality on middle-aged and older adults’ environmental perceptions, leisure activity, and well-being. The Neighborhood Green Space Tool was used to assess the environmental quality of 19 parks, and 380 individuals aged 55 years and older were interviewed in each park using an on-site questionnaire. The results reveal that the associations between environmental perception and well-being were moderated by the quality of park accessibility, amenities, and incivilities; the effect of environmental perception on depression was moderated by the quality of incivilities in parks; and the effect of frequency of leisure activities on depression was moderated by the quality of park accessibility.