Intense transformation and conflicts between different land use types has occurred in the past decades and will still exist in the coming decades in China. Ascertaining the quantity and pattern optimization of urban ecological land is critical to guaranteeing urban ecological security and realizing urban sustainable development. In this study, Nanjing, a very famous city in the Yangtze River Delta in China, was selected as the case study to explore the land use changes from 1995 to 2017 and calculate the suitable amount of ecological land to meet the needs of its socioeconomic development. From 1995 to 2015, the proportion of ecological land in Nanjing dropped from 84.41% to 59.15%. Based on the minimum cumulative resistance model (MCRM), we designed four alternate scenarios to explore the optimal quantity and pattern of ecological land in Nanjing. By comparing the current land use status with the model simulation results, we proposed the suitable ecological land area for Nanjing should be no less than 3963km2, which is 56% of the total area of Nanjing. The land use strategies and the measures to protect ecological land in this study can provide a reliable reference for sustainable development of other highly urbanized regions in China.