Abstract: The paper studies the smooth particle hydrodynamics(SPH) method and establishes rmdel of discharge through crest orifice on dam.The author applies the SPH model to the flow of liquid with free surface on Laxiwa dam,simulates the process of the discharge of the surface outlet.The water recharge boundary is used in the rmdel.The paper gives the an analysis of the numerical pressure and the experimental pressure.The results indicate that it is possible to simulate and research high-speed flow using the smooth particle hydrodynamics method.