n this paper,based on the,flood characteristics and the current status of tile flood control worksin the middle and lower reaches of the Hahjiang River,a bivariate probability model is developed for calculatingthe flood diversion operation frequency of the Dujiatai Project.In this model,both of the upstream flood peakdischarge and the highest water level at the downstream confluence are considered as the independent random variables.By applying the relationship between the safe channel capacity and the confluence water level,then,thedistribution function of peak discharge of diversion flood is obtained.The calculated results with the model areclosely consistent with the observed data.