The reservoirs of Nierji and Fengman are the control projects of the Songhuajiang River basin.The joint applieation ofthe 2 reservois is of great significance for the water resources allocation in the Songhuajiang River basin above the HabinHydromety Station. In this paper，annual indlow series of the Nierji and Fengman reservois were used to build the jintprobability distribution model for the 2 reservoirs based on Copula function. The results show that the wetness-dryness asynchronousfrequency(60.79%) of the 2 reservoirs is significantly higher than the wetness-dryness synchronous frequeney(39.22%) of theFengman reservoir，indicating the inflow condition is helpful for the joint -operation of the 2 reservois; The pobabiliy ofinsignificant conditions for the reservoirs joint-operation is 40.9%;the probability of the favourable conditions for the reservoirsjoint-operation is 43.18%;the probability of adverse conditions for the reservoirs joint -operation is 15.92%，Due to that theprobability of adverse conditions is not low and once it occurs, it will have great inuence on the water supply.Therefore,seriously consideration should be given in the formulation of joint operation plan.