Abstract:The relationship between stage and discharge caused by flood fluctuation shows a clear loop curve and most of the current researches are based on plain rivers. Due to larger river-bed slope, bigger size of sediment the difficult flow characteristics affected by many factors, some assumptions used are inconsistent so that the result is not very accurate. Therefore, this paper, considering the differences of river bed morphology and sediment particle size between mountain rivers and flat rivers, introduces new parameters of equations about river grade and sediment size and reintroduces the new stage-discharge relationship based on Saint-Venant equations. The results of examples application show this method can better fit the actual data of stage-discharge of the cross-sections in mountain rivers and plain rivers. When adapting the line, this method only need to make some corrections to the parameters according to the actual situation, which is more convenient to modify and has good practicality, high precision and strong adaptability.