The invention mainly provides a preparation method of a carbon doped CaV2O4 magnetic composite material. The carbon-doped magnetic composite material is mainly composed of carbon and an antiferromagnetic CaV2O4 material. The main method comprises the following steps of: electrolyzing a vanadium-containing raw material and active material additives in a molten salt for a certain time at a certain temperature, collecting electrolysis products at a cathode, and performing post-treatment to obtain the carbon-doped CaV2O4 magnetic material. The molten salt electrolysis process using the vanadium-containing material as a raw material and added with the active material additives is simple in process, safe to operate and environment-friendly; the high-value carbon-doped CaV2O4 magnetic composite material is prepared, the benign combination of conductivity and magnetism of the material can be realized, and the high-value carbon-doped CaV2O4 magnetic composite material has good wave-absorbing performance in Ku band.