The district of standard runoff were built in the slope land of the Fourth Century Red Soil in order that they could be used in experiments. Through analysis and studying, we simulated the linearity equation between runoff and rainfall, built the power function equation among runoff, the intensity of rainfall and the amount of soil and water erosion. It was got a critical runfall of causing soil and water erosion,and we discovered the common orderliness of soil and water loss at slope land of the Fourth Century Red Soil.