Three typical factors including land desertification, soil erosion and rocky desertification are selected to establish the evaluation model of eco-environmental sensitivity by integrating the technologies of RS and GIS in the present study. This paper conducts comprehensive research on eco-environmental sensitivity, reveals its spatial features in quantitative way and defines the redline of ecological sensitivity in China. The results are as follows: 1) the moderate sensitivity is the main type of land desertification. The surrounding areas of deserts in semiarid areas of northern China are the most sensitive areas. This is due to the strong wind in winter and spring in these areas, and the soil that mainly consists of sand and is seldom covered by vegetation is also the reason. 2) The slight sensitivity and insensitive areas take great proportion in soil erosion. The southwestern and southeastern parts of China and loess hilly regions are the most environmental sensitive areas, which is mainly the result of the abrupt slopes and spatial variation of precipitation. 3) The insensitive area is the main type of rocky desertification. The karst areas of southwest China are the most sensitive areas. 4) The main types of comprehensive eco-environment sensitivity in the study area are slight, insensitive and moderate. The comprehensive eco-environment sensitivity in northwestern, southwestern, southeastern parts of China and loess hilly region is higher than other areas in China. 5) Based on the evaluation results of comprehensive eco-environment sensitivity, taking the extreme sensitive areas as the ecological redline areas, this paper uses top-down method to define the redline of eco-fragile areas in China. Three types and 23 important ecological redline areas are delimited across the country, and the ecological redline areas make up about 12.86% of the study area.