Abstract: By analysis of the data of field simulated rainfalls, this paper makes the conclusion that in the Loess Hilly Region, the critical rainfall intensity that can distiguish the two main runoff-production modes on grass and bushes ranges from 1.40 mm/min to 1.45mm/min. And on bare sloping field, the critical rainfall intensity that make sharp transfomation of sediment-yield intensity ranges from 1.50mm/min to 1.53mm/min. At the same time, this paper talks over the sediment-yield charicterdistics of different land use, and finds their corelative equation. Results indicate the great benefits of vegetation on decreasing slope soil erosion.