From the small watershed data since libration and materials in experimental runoff plots under different controlling measures in early 1970's as well as precipitation, the connotative relationship between precipitation and soil and water loss was found by frequency and mathmatical statistics and analysis. The result showed that the soil and water loss in small watershed could be estimated by precipitation regression equation, and in experimental plot by experimential model with main component method, which provided a scientific basis for soil erosion and loss research as well as small watershed comprehensive control.