Abstract: In order to determine the primary erosion factors influencing soil detachment rate, the runoff wash out test was conducted in varing slop soil with the range of slope gradient from 9° to 24°and discharge from 2.5 L/min to 6.5L/min). With the method of stepwise regression analysis, therelationship between soil detachment rate and water erosion factors such as slope, discharge, runoff shear stress, stream power and unit stream power and unit energy consume was studied systemically. Based on stream power and slope, binary linear equation for soil detachment rate was determined with the detemining coefficient of 0.977. The results show that significant correlation exit between soil detachment rate and discharge and slope, runoff shear stress with the detemining coefficient of 0.77, 0.908, respectively. Soil detachment rate increases linearly with the stream power increasing with detemining coefficient of 0.945. Linear relationship exists between soil detachment rate and unit runoff energy consumption with detemining coefficient of R2=0.91. Third-order relationship exits between soil detachment rate and unit stream power with the detemining coefficient 0.52. Stream power and slope are the primary erosion factors influencing soil detachment rate.