In order to make the parameters of the water quality model more realistic and reduce the equivalent phenomenon of different parameters in water quality model, this paper proposed a method to identify the model parameters by setting laboratory experimental constraints, which could be used to make a certain degree of internal process control. The example of a water quality simulation by WASP model in a section of the North Canal showed that by this method, the model could be more accurate to reflect the actual water quality change process by reducing uncertainty and equivalent from combination of the parameters. Through the action of the nonlinear model structure and constraint conditions, the originally independent parameters under the same sub module began to demonstrate certain correlation. With the further study of the water quality change process, the constraint conditions would be further enhanced when introduced new constraint conditions or fault decrease tolerance.