Through the application of double summation curve, Zhifanggou watershed of Pingliang City was chosen as a research site to analyze the periods of discrepancy appearance of soil erosion character under the background of large-scale comprehensive water loss and soil erosion treatment from1981to 1997. The result indicated that soil and water loss condition and treatment changed sharply in 1985. Owing to the increase of treated area and the enhancement of comprehensive management extent, the relationship amongst precipitation, runoff and transported sand has been improved obviously since 1985. Meanwhile, It is also found that there is linear correlation between precipitation, discharge, treatment extent and soil erosion loss at a certain extent.