Abstract: The propagation, reflection and diffraction of 2-dimensional dam break wave are studied by solving the shallow water equations with a Godunov's scheme which is derived in detail. The compact expressions of Hc,d and Vo,d2, the contact discontinuity of water surface elevation and velocity at the boundaries of general cells are also given to complete the calculation. The numerical results are quite satisfactory compared with the measurements and the 1-dimensional analysis, so they are useful for the dam design...