The invention discloses a preparation method of a porous graphene-ferric oxide composite material, which comprises the following steps: (I) dissolving graphene oxide and iron salt as raw materials into water at a certain mass ratio and uniformly mixing; (II) separating the graphene oxide out of the liquid mixed in the step (I) through centrifugation or suction filtration, and cleaning by use of water or alcohol; (III) re-dispersing the product obtained by the step (II) into the aqueous solution, and performing freeze-drying treatment on the product; (IV) performing heat treatment on the product obtained by the step (III) in air or oxygen to obtain the porous graphene-ferric oxide composite material, wherein the heat treatment temperature is 300-1,000 DEG C, and the heat treatment time is 10 seconds to 10 hours.