Abstract: Based on artificial rainfall simulation experiments, the variation of runoff and sediment were obtained under the condition of the different soil surface roughnesses and the continuous rainfall. Results show that runoff is delayed for the case of the different soil surface roughnesses with the rainfall. The function is relatively obvious to the soil surface with artificial hoe. However, it appears only to the initial rainfall stages. The variation laws of runoff are the same with the rainfall. The runoff increases at the early stages and becomes stabilization gradually. The total runoff amounts do not change notably for the sum of the five rainfall applications. The amounts of sediment at the 15° slope surface are greater than those at the 5° slope surface. The variation is more obviously during the condition of the rainfall density of 1.0 mm/min. The total amounts of sediment do not change obviously with the rainfall. From the above, effects of soil surface roughness on soil erosion have the relationship not only with rainfall duration but also with slope gradient, and the critical conditions to soil surface roughness effect on erosion are approved preliminarily in Loess Plateau. The results would provide theory basis for revealing the nature of roughness, and at the same time, it would serve for harnessing soil and water loess and reclaiming forest and grass from farmland in Loess Plateau.