This paper contributes the considerations.methods and illustrations of the calculated discharge computed with a variable characteristic difference method,if the condition of the hydrological station is conformed to the follows t unsteady flow in open channel with one dimensional stable riverbed,then,the discharge hydrograph can be derived from the water level hydrograph actually measured from two sections.Comparative analysis of the theoretical computation of discharge hydrograph vs.actual one is also presented in this paper.Results obtained from Sihong and Yunhe Stations show that the calculated discharge is basically conformed with high precision to the actual measurements.The method presented here has the following meritsxsafe and reliable,saving man-power and material resources,high measuring precision.avoiding missing records and making mistakes in high flood period so as to ensure the flood data to be continuous and complete.The method can also be adopted for lakes in their water balance computations by employing two groups of gauges without any special discharge measurement station.