The invention relates to a graphene foam loaded nano Fe3O4 magnetic particle composite wave-absorbing material and a preparation method thereof. Graphene oxide is prepared according to a Hummers method, graphene oxide colloidal suspension with a certain concentration is prepared, an Fe2+ solution is added, after the pH value of an ammonia-water solution is adjusted, the ammonia-water solution is injected into a reactor, and reaction is carried out under the high-temperature, high-pressure and closed condition. Fe2+ solubility, pH value, reaction time and reaction temperature are adjusted to adjust the foam holes and the wave-absorbing property of a composite material. Graphene in the graphene foam loaded nano Fe3O4 magnetic particle composite wave-absorbing material has a foam multi-hole structure, Fe3O4 magnetic particles are firmly anchored and loaded in the graphene foam structure, and the grain size of Fe3O4 is 150-300 nm. The graphene foam loaded nano Fe3O4 magnetic particle composite wave-absorbing material is high in absorbing strength, wide in wave-absorbing frequency bandwidth, light in weight and good in mechanical property, and is a composite material with excellent performance. Multiple aspects of use requirements can be met.