The underwater electrical wire explosion（UEWE） is an effective way to obtain strong underwater shock wave（SW）. In this paper

a double-lens 4 f imaging system was used to reduce the phase difference and a series of laser-backlight shadow images of underwater electrical explosion of copper wire were captured. Combined with the waveforms of electrical signals

the evolution of shadow images was described and analyzed. It is found the first distinct pressure wave is produced before the end of melting

which shows a multilayer structure in the shadow image. This pressure wave propagates at a speed close to the sound velocity in still water

and is then chased and submerged by the main SW. During the vaporization stage

the early distribution of water flow leads to a blurred shadow image boundary. The explosive wire and the main SW show good axial uniformity with smooth and neat boundaries. Based on the measured expansion trajectory of explosive wire

the simulated propagation trajectory of SW is highly consistent with the experimental results. Some important physical information

such as the shock wave form and the pressure of the explosive wire

can also be calculated by the model.