Abstract: With three structural steels of Q235A low carbon steel, 16Mn and 15MnVN low-alloy steels, respectively, as a basal plate and 304 stainless steel as a shroud plate, the structural steel-stainless steel composite plates were prepared by explosion welding. The microscopic defects at the bonding interface were investigated by ultrasonic flaw detection, scanning electron microscopy, energy dispersive spectrometer, etc. The results show that the holes and the microgaps existed at the interface of explosion-welded composite plates, which can't be eliminated by hot-rolling. The main element was iron in the holes and the composition was much different from that of raw steel plate. The microcrack ratio in the interface of the explosion-welded composite plate increased with the increase of the explosion speed or the reduction of the plasticity of the basal plate. After hot-rolling, some sandwich defects were found in the local interface of the composite plate, which were on the side of the shroud plate and with nearly the same composition as the basal plate.