The invention relates to the field of alloy materials, in particular to an alloy composite body and a manufacturing method and application of the alloy composite body. The alloy composite body comprises a steel board layer, a metal binding agent layer and a nano-cemented carbide material layer, wherein the steel board layer is combined with the nano-cemented carbide material layer through the metal binding agent layer; and the nano-cemented carbide material layer contains 40-65 wt% of coarse particle tungsten carbide, 20-45 wt% of nano-particle tungsten carbide and 5-40 wt% of cobalt with the total weight of the nano-cemented carbide material layer as the benchmark. The mechanical strength, hardness and abrasion resistance of the alloy composite body are very excellent, and when the alloy composite body is used for detaching toothed chains of maintenance and cleaning cars of rail tracks, the hardness and the mechanical strength of detaching toothed heads can be improved remarkably, and the service life of the detaching toothed heads can be prolonged remarkably.