Based on the analytical framework and calculation principles of the CITYgreen model to assess the benefits of urban green spaces in terms of carbon fixation and runoff reduction, an approach was made to obtain appropriate parameters for this model to calculate the ecological benefits of different urban land use types in the main city of Nanjing. The results indicate that carbon fixation benefits received by the main city of Nanjing is 5%-60% of that by natural forests on a per unit area basis. The ecological value of carbon fixation and runoff reduction of the Nanjing urban green space was about 177 million RMB in total. The ecological benefits of different land use types were in the order of green area > public facilities > residential areas > roads and squares > industrial areas > municipal utilities. This research can provide references for city planning and urban green space establishment and facilitate the popularization of quantitative assessment of ecological benefits of green spaces in Chinese cities.