A performance index is defined for linear wave dispersion property. The index measures the capability of a water wave model to simulate irregular wave transformation over general topography.Optimization of this index leads to:(1) the optimum vertical distribution functions for the nonlinear mild slope equations given by Isobe (1994) for different number of vertical distribution functions,(2) the optimum values of wave numbers to be used for the fully dispersive nonlinear wave model given by Nadaoka et al. (1994) for different number of vertical distribution functions,(3) the optimum values of the wave number to be used for the time dependent mild slope equation given by Kirby (1984). All optimized parameters are given as functions of the dimensionless peak frequency of the energy spectrum. Comparisons among the optimized models are given.