The dissertation utilizes the measured sandy soil values as a basis before the basin is sandcontrolled,and then by using these topological forecasts decides the theoretical sandy soil values during the basin is sandcontrolled. Comparing with values,we can get a new method to detect the basin decreased sandy soil benefit of its ground and its fields. By taking the Yanhe basin as an example and contrasting with both the waterandsoil conservative way hydrlogic way,we gain a satisfactory conclusion.