Energy-saving reconstruction of old residential buildings is a vital way to achieve sustainable development, but the potential of rooftop photovoltaic (PV) energy-saving in old residential buildings has not been studied. This study established a basic framework for the estimation of rooftop PV technical, economic and environmental potential in the old residential buildings of Nanjing City, and provide the prediction results for the development of rooftop PV development plan in Nanjing. We estimated the available area, maximum electricity generation, environmental and economic benefits of rooftop PV in five districts of Nanjing by using building roof profile data, calculation method of maximum solar radiation at optimal tilt angle and GIS method. We find that the electricity generation potential of installing rooftop PV in the old residential buildings in the study area would meet about 17.7-20% of the residential electricity demand under three scenarios of the PV performance ratios (PR). Additionally, the carbon reduction potential of the life cycle rooftop PV reaches 13912874.12t (PR = 0.85), 13094469.76t (PR = 0.8), and 12276065.4t (PR = 0.75), respectively; and the result of economic potential shows that the life cycle of rooftop PV cannot generate economic benefits with an NPV value less than 0. The feasibility analysis framework provided in this paper can be applied to the assessment of rooftop PV potential in other cities in China, and provide valuable advice for the rational planning of rooftop PV.