Abstract: Blast wave produced by an outer-sphere charge exploding in water of infinite depth was numerically simulated by solving the one-dimensional hydrodynamic equations for an inviscid and non-heat-conducting flow.In the simulation calculation, a Jones-Wilkins-Lee equation of state for TNT and a two-phase equation of state for water were adopted. The interface between the explosion products and water was determined by using the level set method.Firstly, grid-size effects on the convergence of the calculated results were explored. And the characters of pressure and impulse of underwater blast wave in the short range were investigated in detail. Finally, the approximate formulas for the peak pressure, specific impulse and attenuation constant were obtained by curve fitting.