Abstract: In order to investigute metal physics mechanism of explosive welding,the bond interface of 321-15CrMoR composite plate by explosive welding was researched by optical microscope(OM),scanning electron microscope(SEM),electron probe microscope analysis(EPMA)and microhardness tester(MHD).The results show that waveform appears in the interface and violent plastic deformation occurs.There are adiabatic shearing bands(ASBs)on the side of 321,which has locally developed to microcrack.And white luminant strip is found in the wave crest.Both ASB and white luminant strip is composed of ultrafine isometric grains.The atoms near the interface diffuse at short range or do far when melting.Besides,there are microstructure such as crack,gas porosity,looseness and so on in the interface.The microhardness increases remarkably near the interface.All the above ensure quick and high quality metallurgical bonding between flyer plate and base plate.