WC steel bond hard alloy powders were compacted by explosive compaction on the surface of carbon steel, then the composite layer was prepared by liquid-phase sintering in vacuum. The phases and microstructures of the interface of composite layer were observed by SEM, EDS, TEM. Result showed that the thickness of the interface was about 30μm, and the elements of W, Cr, C were detected in the interface. The structures of the interface were pearlites which were composed of the layered tablets of M23C6 and ferrite. The layered tablets were perpendicular to the interface. The structures were the pearlites and ferrites in the side of the carbon steel near the interface but globular carbides, whose phase is W3Fe3C, and pearlites in side of steel bond hard alloy. During sintering at 1623K, all elements of metal-powder and C, V, which were decomposed by hard-phase, interdiffused in the interface. The multiple carbides were found in the interface and steel bond hard alloy. As a result, the powders formed into compact alloy by itself, and at the same time there was a good metallurgical bonding between the carbon steel and the hard alloy.