The invention belongs to the technical field of functional nanomaterials, and particularly relates to a preparation method for a sandwich-structured cobalt-nickel alloy particle/reduced graphene composite material. According to the preparation method, graphene oxide is selected as a carbon base for the chelation and growth of cobalt-nickel ions, and by changing the varieties of chelating agent andPH regulator and the concentration of precursor solution, cobalt-nickel alloy particles, the size distribution of which is 0.2 Mum to 1.2 Mum, are prepared, and are chelated and dispersed onto the surface of reduced graphene; and then, by subsequent freeze-drying, the sandwich-structured cobalt-nickel alloy particle/reduced graphene composite material is obtained. The composite material shows excellent loss performance in the field of microwave absorption, in particular, when the average size of the cobalt-nickel alloy particles dispersed in the compound is 0.8 Mum, the maximum microwave losscan reach negative 54.4 dB (the submicrowave absorption peak is negative 45.4 dB), the bandwidth is up to 4 GHz, and as a novel microwave absorption material for microwave absorption, the sandwich-structured cobalt-nickel alloy particle/reduced graphene composite material has a broad application prospect.