Abstract: In order to understand the impacts of urban development on the ecological environment, based on the ASTER Remote sensing image data of Nanjing City in 2002, 2014 and 2017, this research used the maximum likelihood method, neural network method and support vector machine classification method to classify the land cover, and chose the highest accuracy method. Then we evaluated the ecosystem service value of the main urban area of Nanjing by the equivalent factor method. Finally, based on the actual situation of Nanjing, this paper analyzed the driving factors from the perspective of population, economy and policy. The results showed: 1) Land cover: from 2002 to 2017, the area of cultivated land in the main urban area of Nanjing City decreased significantly, most of which were transferred to construction land and a small part to woodland. 2) ESV: from 2002 to 2017, ESV decreased by 181 million yuan, of which farmland decreased by 304 million yuan, grassland decreased by 57 million yuan, and forest land increased by 194 million yuan. In terms of single function, water conservation and waste treatment had the highest benefits, accounting for nearly 60%. In addition, ESV was the most sensitive to water, and grassland was the least sensitive. The influence of farmland on ESV was less and less, while that of forests was increasing. 3) The economic development of the main urban area of Nanjing had a negative impact on its ecological environment. There is a slight conflict between the ecology and economy in the main urban area of Nanjing, and the conflict is slightly intensified with the passage of time. The main reasons for the decrease of farmland area and ecosystem service value were population growth and economic development, urbanization of marginal areas, decrease of the proportion of primary industry and increase of the proportion of secondary and tertiary industries. The influence of policy factors such as ecological engineering has been the main reason for the increase of forest area and forest ecosystem service value in the main urban area of Nanjing. In the past 15 years, in the process of its own development, the increase of population and the development of economy have led to a large amount of cultivated land occupied, which makes the ecosystem service value of Nanjing obviously declined. Strengthening the construction of ecological engineering can make up for the loss of ecosystem caused by urban development.