Abstract: The complex mechanics-energy causes behind the boundary effect of explosive welding are discussed, and the mechanics-energy principle is systematically expounded. Under the guidance of this principle, the reason for the elongation deformation of the composite plate is clarified, and the technical problem of strong hardening and cracking in the middle of the base plate during the two explosive welding of the large composite plates is solved, so that this mechanics-energy principle has been fully demonstrated and skillfully applied. Both theoretical analysis and practical results confirm the correctness of the principle, which is worthy of flexible application in production practice.