The underwater electrical discharge forming method makes use of energy generated by an impulsive high current discharge across a pair of electrodes, which are usually bridged by an initiating wire. It is necessary to consider various phenomena for the study of this process, such as the exploding wire phenomena, generation and propagation of shock waves, interaction and reflection of the waves at the workpiece and the behaviour of workpiece deformation. The magnitude and form of the pressure waves propagated in water have a particularly significant influence on the deformation process. It is difficult to apply numerical analysis to the underwater hydrospark forming process because of many unknowns, such as the form of the pressure wave, the conversion mechanism from pressure wave to stress wave and the stress-strain characteristics at high strain rate. Numerical analysis have been carried out in the past by assuming a particular pressure wave form at the surface of the workpiece, but the problem has not been solved with consideration of the interaction between water and workpiece. In the present paper, a finite element method was applied to the electrohydraulic forming of circular tubes, with consideration of those interactions. Comparison was made with the experiments. The results obtained were qualitatively in good agreement with the experimental ones.