Two dimensional numerical simulation of the boundary effect in explosive cladding was carried out by using the LS-DYNA software and gridless Smoothed Particle Hydrodynamics (SPH) method. Results show that the phenomena of metal jet and boundary effect were consistent with the production practiof explosive cladding. The reason of causing the boundary effect in explosive cladding is not caused by the damage and cracking at the boundary when colliding of the base composite plate due to the excess impact energy of the boundary, before the base composite plate collision, the fracture has been generated. Considering that The generation of boundary effect in explosive cladding is due to the effect of rarefaction wave on the detonation products at the boundary, leading to the velocity difference is existed at the boundary and internal of composite plate, so that the collision angle at the boundary of composite plate becomes bigger, the frature occurs under the action of detonation pressure. In addition, the boundary effect can be effectively controlled by using honeycomb structure explosive and double sided detonation composite method.The preventive measures are proposed to against such a phenomenon.