This paper presents a weakly nonlinear water wave model using a mild slope equation and a new aplicit formulation which takes into account dispersion of wave phase velocity,approximates Hedges'(1987) nonlinear dispersion relationship,and accords well with the original empirical formula.Comparison of the calculating results with those obstained from the experimental data and those obstained from linear wave theory showed that the present water wave model considering the dispersion of phase velocity is rational and in good agreement with experiment data.