The characteristics of non-linear San Venant equation solutions and their stability and astringency with Preissmainn format considering the influence of resistance were analyzed，and then relations between numerical solution astringency and Δt/Δs and L/Δx in different φ and θ was also discussed. At the end, it's pointed out that attenuation and dispersion were always exist, and it's important to choose appropriate φ and θ in order to control numerical solutions' dispersing range and modeling velocity in actual model.