Abstract: The paper applied the WEPP model, which is the most complicated soil erosion-forecasting model to predict the rainfall corroding, and contrast with measured value, though the observation on the runoffs and sediments of Suining group purple soil, then contrast the influence to the forecasting value between the climate generator and breakpoint climate data generator. By way of analyzing to the result, thinking that the WEPP model applying on the group purple soil erosion is reasonable, and the forecasting result of using the breakpoint climate data generator is superior to use the climate generator.