The invention discloses a preparation method based on a solid-phase reaction for a capacitor electrode material. The preparation method comprises the following steps of: 1) adequately mixing and grinding cobalt acetate, oxalic acid and oxidized graphene to obtain an cobalt oxalate-oxidized graphene mixture; and 2) calcining the cobalt oxalate-oxidized graphene mixture aforementioned to obtain a cobaltosic oxide-graphene electrode material, wherein the dosage ratio by mole of cobalt acetate to oxalic acid is 1: 1, and the dosage of oxidized graphene is 5-30% of the mass of the finally obtained cobaltosic oxide; additionally, the selected ligand can also be citric acid and hexamethylenetetramine except oxalic acid; a solvent is not used in the solid-phase reaction of the preparation method disclosed by the invention, so that the side reactions generated in a water-phase reaction are avoided, the yield and the purity are increased, the reaction conditions are easy to control, and the operation is simple and practicable; and moreover, via the introduction of the graphene material, a novel way is provided for an oxide material with bad electrical conductivity, good energy storage property, and high theoretical specific capacitance in the field of capacitors, and the graphene material has important theoretical and practical application significance.