Underwater sparks have long been used in many fields, but up until now there are no widely accepted model for them. In this article we present a more practical model for them, taking into account the nature of the plasma of pulsed discharge in water, where the following corrections are included: (1) correction of the ionization potentials; (2) pressure caused by the effect of charge interaction on the bound state electrons; (3) line spectra; and (4) mass flow caused by evaporation, condensation, and bubble wall ablation. Using this model, the time-varying pressure, temperature, and density can be obtained for given circuit parameters. The simulation results are in good agreement with the experimental measurements. We also give a simulation with capacitance of 1.25 nF, initial voltage of 4x10(4) V, circuit inherent inductance of 20 nH, and circuit resistance of 15 m Omega; the maxima of the pressure, temperature, and electron density are about 5x10(4) K, 5x10(3) atm, and 4x10(26) m(-3), respectively. (C) 2002 American Institute of Physics.