Abstract: In order to reduce the numerical diffusion error of the convey-diffuse equation, the concept of concentration on cross section is introduced to calculate the mean concentration of river sections, and a new finite control volume method is put forward based on the incomplete mixing pattern.Depending on above concept, a income water component model is set up, which simulates the water source composition of the basin and describes the spatio-temporal changes of different water sources.By applying the present method in calculation, the results are in agreement with the measured data, indicating that the present method of incomplete mixing pattern can improve the accuracy of income water calculation.