The invention discloses a preparation method of a magnetic graphene composite material. According to the magnetic graphene composite material, magnetic nano particles are modified on a graphene nano sheet, and the characteristics that graphene has high adsorbability and a magnetic material is convenient to separate are combined to form a novel magnetic nano biological adsorption material. With the adoption of the preparation method, the disadvantage that the graphene material is easy to reunite is overcome, the specific surface area of the adsorption material is greatly enlarged, binding sites of the adsorption material are increased and an adsorption object range is enlarged. The preparation method of the magnetic graphene composite material is simple, low in cost, and stable in physicochemical properties and can be repeatedly used; and simple and feasible methods and manners are provided for achieving environment wastewater treatment and waste recycling.