Soil erosion generated by road construction project is significantly serious.Based on the calibration of the characteristics of rainfall simulator , side slope of different gradients and different degrees of compactness formed in road construction process is studied.Results show that soil erosion is aggravated with increased slop gradient.Soil erosion rate reaches a peak at about 25° , beyond which it begins to decrease and finally goes to a steady state.Moreover , soil erosion is alleviated with increased soil hardness and this trend is more obvious if rainfall intensity becomes much stronger.Additionally , soil erosion is aggravated with the increasing of antecedent soil water content.This study may provide a basis for the scientific evaluation of soil erosion on earth side slope in an engineering project.