Based on field investigation in the typical areas,the gradation of potential soil erosion danger is carried out by using GIS technology.Compared with the index of soil erosion potential danger(SEPDI) of two different periods in 1990 and 2005,purple soil erosion potential danger in Wanzhou District,Chongqing City is analyzed.Results show that by the guideline with Ministry of Water Resources' classification standards,the potential danger of soil erosion may be divided into three grades.The SEPDI in 1990 year is 2.05 and the SEPDI in 2005 is 2.07,which indicates that the SEPDIs of two different periods do not have a remarkable change.By analyzing soil erosion potential danger in the two periods under such influence factors of soil erosion as land use type,vegetation cover,gradient level,and soil thickness,the spatial distribution of soil erosion potential danger is evaluated.At last,the paper summarizes that the causes of soil erosion are the local geographical features,large scale migration,and irrational measures of soil and water conservation.