On the basis of data obtained from field investigation and the meas-urement of topographical map, the present paper dealt with the originof soil erosion in a certain small watershed in Chunhua Model County.The relations among soil erosion and erosion causes are shown by the for-mula E= f(J·ρ·C·S). It was found by relation analysis among erosive mo-dulus and erosion causes that topographic grade, channel frequency, thenumbers of active gully head, the vegetation coverity of slope, and thesize of watershed area had close relations to erosive modulus. However,the forest coverage and the level of Yuanmian control did not have closerelation to erosive modulus. It was considered that those results werecaused by few measurements, low level, poor quality, nonorganizationsystem of soil and water conservation practices nowadays in the area.