The invention provides a preparation method of RGO/Cu (reduced graphene oxide/copper) nano composite powder. The preparation method comprises the following concrete steps: reducing graphene oxide, and uniformly loading copper onto graphene by sensitizing and activating methods to obtain the nano composite powder with copper uniformly loaded on a graphene sheet layer. The preparation method comprises the steps of sensitizing and activating graphene, preparing an intermediate product of the RGO/Cu nano composite powder, and reducing the RGO/Cu nano composite powder by H2. The method provided by the invention is a brand-new method for preparing the nano composite powder with copper uniformly loaded on graphene sheets, and has the advantages of high efficiency, quickness, simple and convenient operation, low cost, no expensive instrument, energy conservation and the like.