There are so many environmental background factors in soil erosion region,such as slope,land use,DEM,etc.However, not all factors play a role in soil erosion equally.Problem about how to identify the main factors in water erosion in China are discussed.Firstly, according to the conditions of study area, environmental background factors that are translated into 100m×100m data format in GRID are choosen.Secondly, degrees for each factor according to the difference degree to soil erosion are set.Each environmental background has different degrees.Thirdly, with the MGE and GIS, we resample in study area in China in equal distance, so that we get lots of samples that can illustrate the study area.Then according to actualsi tuation of each sample, values are put into each sample in line with degrees in the step 2. Finally, all datum are put into software package SPSS for factor analysis.Through factor analysis, the main factors can be choosen.This model is based on expert knowledge and object analysis, overcoming the man-made factor and showing the situation objectively.