The rainfall, runoff, soil content in water on the hilly area of the central Sichuan basin have been stud- ied in paper, debited the mathematic mode forecasting the sand and soil eroding. There has been analyzed connec- tion to the differing forests types with by the numbers and synthetically. What's more, parallel synthesis the law of the loss about the sand and soil. It is studying the sand and soil loss that make protect the sand and soil on the hilly area of the central Sichuan basin, so the law can help farmers to change the protect forests in the future.