The invention provides a preparation method of graphene powder, relates to a preparation method of carbon structural materials, and solves the problem that the traditional preparation method of the graphene powder can not be easy to store and transport, simple in operation method, low in cost, continuous to produce and environment-friendly synchronously, and also solves the problem that the grapheme made by the present method has many defects and high energy consumption. The preparation method comprises the following steps: grinding and mixing to prepare the mixture powder of magnesium powder and carbonate powder; and burning and synthesizing the mixture powder, thus obtaining the graphene powder. The preparation method of the graphene powder provided by the invention has the advantages of being easy to store and transport, simple in operation method, low in cost, continuous to produce and environment-friendly; the prepared graphene powder is low in default, and is thinner; and the preparation method provided by the invention is suitable to be applied to industrially producing graphene.