This paper applies the level set method in combination with the three dimensional incompressible NavierStokes equations to simulate dam break flows. The finite difference method is employed to discretize the governing equations and the projection method is used to derive a pressure Poisson equation that can ensure the satisfaction of continuity equation. In addition, the WENO method may solve the space discrete items of the level set equation. Finally, a 3D dam break computation is presented. The simulated results are in excellent agreement with experimental data. The numerical model is demonstrated to be successful.