Against the backdrop of rapid population aging and significant demographic changes, cities are facing great challenges in providing healthcare resources for the elderly. Understanding the equity and spatial differentiation mechanisms between the demand and supply of healthcare resources for the elderly in cities, especially in rapidly urbanized areas, can help policymakers to promote the planning and construction of a ‘Just City’ and ‘Age-Friendly City’, safeguarding the human well-being of the elderly. This study combines outpatient appointment data classified by service type with community-scale demographic data to assess the equity in the supply of medical resources for the elderly in the city using a refined two-step moving search method. Taking Xiamen City as an example, we analyzed the spatial heterogeneity in the equity in the supply of different types of health care services for potential elderly patients in each community in the city. Then, we selected six driving factors to explore the underlying driving factors. The results showed that there were 308 communities (61.11%) with a high medical service balance of the internal medicine type for the elderly in Xiamen City, concentrated in the southwest of the whole area. There are only 157 communities with high medical service balance for the surgical type of medical services, concentrated in the central part and southwest of Xiamen City. For these two types of medical services, the number of communities with low medical service balance is 30 (5.95%) and 182 (36.11%), respectively. These communities are far away from the central city. Economic vitality is the most important driving factor in the spatial distribution pattern of equity in the balance of medical services for the elderly. Our study can provide quantitative information on the current situation evaluation and decision support for the development and design of a ‘Just City’ and ‘Age-Friendly City’ Planning.