Abstract: By modelling the two-port network of the water transition system for a pumped storage power station, the B-spline fitting method is used to fit the water turbine wheel of water pump, the water transition system and the hydraulic model of the unit are built, and the calculation results of the new model are compared with the real machine test data, based on which the effectiveness of this model and its fitting method is verified, offering a new means for the study of transition process of pumped storage power stations.