In present, sediment model research is usually focused on cases of small basin with short time interval record of rainfall and high density network of rainfall gauging station. There are two problems come usually across in the application of such model to middle and large scale of basins, that are time and space scale problems. A middle scale basin with high density network of rainfall station and six small scale basins with short time interval record rainfall were chosen. The relations of simulating accuracy respectively to time interval scale and to space scale were then analysed in turn. And finally, some useful conclusions were obtained.