Abstract: In order to reveal the mechanism of explosive welding boundary effect, LS-DYNA software and meshless SPH method is used to carry out two-dimensional numerical simulation of explosive welding boundary effect on TA2/Q235, Q235/Q235, Q235/TA2 and 304 stainless steel/Q235 composite plates respectively in this paper. The thickness of the flyer plate is 2 mm and the thickness of the based plate is 16 mm. By observing the flight attitude of the flyer plate in different simulation groups, it revealed that the tearing of the flyer plate occurs before the collision with the base plate. When the base plate is consistent and the explosives are emulsion explosives and expanded ammonium oil mixed explosives, the tearing size of the TA2 is larger than the Q235 steel and 304 stainless steel. When the base plate and flyer plate are made of Q235 steel, the tearing size of the flyer plate under the condition of emulsion explosive is larger than that under the condition of expanded ammonium oil mixed explosive. The above results show that the boundary effect of explosive welding still exists when the flyer plate and explosive change, but the severity of the boundary effect is different. The lower the ultimate tensile strength of the flyer plate or the higher the explosive velocity, the more serious the boundary effect phenomenon.