The large-scale convergence of homotopy parametric inversion method on the water quality model parameters calculated was used, with application in parametric inversion calculation of total phosphorus of Beijing Miyun Reservoir. Through calculated and compared the error of sedimentation rate by homotopy parametric inversion method and genetic inversion calculation method, the results indicate that homotopy parametric inversion method has good stability, calculating speed, and even if the initial selection away from the objective function, the solution still has a good convergence.