This parer uses integration to deduce a set of formulas of calculating time-average sedimentdischarge based on that the changes of discharge and sediment concentration are linear but the change of sedimentdischarge is quadratic. It is considered in this pater that it is reasonable and practical to use this set of formulasin calculating daily average sediment discharge and daily average percentage of sedimient smaller than a certaingrain diameter, which can improve the accuracy of the result.