Urban green space plays an important role in providing ecological and social benefits. The rapid advancement of urbanization has led to increasing social stratification and inequitable access to public green space resources for social groups, especially the elderly. For this reason, 340 parks in 133 streets in the main urban area of Beijing are taken as the research objects, and the park green space supply model is improved to evaluate the fairness of urban park green space supply based on the relationship between supply and demand, etc., and put forward the optimized layout plan of park green spaces. The results show that: (1) The improved park green space supply model fully takes into account different park types and park quality. (2) The total park green space supply in 46.6% of the study area fails to meet the demand of the elderly, clustered in the second to fifth ring road of Beijing; compared with the other three park green space types, the elderly have more opportunities to enjoy the supply of community parks and greenspaces. (3) The supply of parks and green spaces enjoyed by the elderly failure to meet the bottom-line requirements of social justice Adding new park green space in Haidian Street, Shangdi Street, and Datun Street and upgrading the park quality of Wangjing Park and Ditan Park are effective means to promote green space equity. The results of the study can provide support for decision-making on optimizing urban park green space and provide a reference for urban refinement management.