Combining the statistical data and the remote sensing data in Nanyang, China, the water source of the Middle Route Project of South-to-North Water Transfer, we selected 16 key indicators to construct ecological security assessment system from three aspects of ecological pressure, ecological status and ecological response.. This system was established by GIS platform and Pressure-State-Response (PSR) model. We evaluated the ecological safety level of the three dimensions of Nanyang City-Danjiangkou Reservoir Catchment Area-Water Canal Buffer Zone in 2000, 2010 and 2015, and analyzed its temporal and spatial evolution characteristics. Results showed:(1) In 2000, 2010 and 2015, the mean values of the Ecological Security Index (ESI) of Nanyang City were 48.88, 49.76, and 50.60, respectively. The mean values of ESI in the catchment area of the Danjiangkou Reservoir were 51.52, 52.80, and 53.70, respectively.The average ESI values of the buffer zone of main canal were 47.98, 49.57, 51.02. Resculs have shown a slow increase trend, and the overall ecological security level of Nanyang City has improved. (2) From a spatial perspective, the ecological security level of Nanyang City from 2000 to 2015 showed a trend of high in the northwest and low in the southeast. The western region of Nanyang showed an overall increasing trend, and the eastern showed a decreasing trend. (3) There are obvious regional differences in the ecological security level of various administrative units in Nanyang City. From 2000 to 2015, the largest average ESI was Xichuan County, and the smallest was Xinye County. There were 6 districts in general safety levels, and 6 districts in lower safety levels. The level of ecological security of Xichuan, Neixiang, Dengzhou and Nanyang city area have been significantly improved. The level of ecological security in Sheqi County has been significantly reduced. (4) The overall correlation between the ecological security level of Nanyang and the ecological status indicators is relatively high, but the correlation with the ecological response indicators is low. The research results can provide references for the ecological safety construction and planning of other cities in the water source area of the South-to-North Water Diversion.