The characteristics of the new explosive welding technique using underwater shock wave developed by some of the authors are demonstrated based on the numerical simulation using AUTODYN. The welding method is effective in accelerating a thin metal plate uniformly at a high velocity. But the welding condition should be different with horizontal position because of the use of high-explosive requests inclination of the explosive to decrease the horizontal collision point velocity. The method to obtain the wavy structure with uniform wavelength is discussed by changing the thickness of explosive.