The hydrological principle of the structure and parameters of watershed hydrological models, the physical coupling relationship between the structure and parameters, and the essential difference between lumped and distributed watershed hydrological models were investigated. The characteristics of the solution methods for these two models, and the reasons causing the phenomenon of equifinality for different parameters during the calibration of the watershed hydrological models, as well as methods to alleviate the effects of this phenomenon, are discussed. A method for verification and comparison of the watershed hydrological models is proposed.