In this paper,the“three defense lines”system of integrated soil and water loss control in Beijing City is analyzed according to the topographical conditions and human activities. At the same timethe envi-ronmental effects of the“three defense lines”are studied. The analysis of soil loss indicates that the spatio-temporal distribution of soil loss is basically consistent with the change of rainfall erosivity. However,there is a greater difference in the magnitude of the spatiotemporal distribution as changed with the spatiotemporal distribution of rainfall erosivity.The change of annual soil loss in Fangshan,Mentougou,Changpingqu,and Huairouqu districts is less,and the change in Miyun,Pinggu,and Yanqing counties is relatively greater.