The invention relates to a suspension polymerization preparation method of a polystyrene-coated ferriferrous oxide composite particle. The method comprises the following steps: placing a n-octane solution in a water bath, adding a mixed solution of ferrous sulfate and ferric chloride, then adding sodium oleate and ammonia water to carry out reactions to obtain oil-soluble ferriferrous oxide; mixing the obtained ferriferrous oxide, polystyrene, and benzoyl peroxide under supersonic waves to obtain a mixed solution, adding a dispersant and deionized water, carrying out reactions for 4 to 6 hours at a temperature of 90 DEG C, washing, separating, and drying so as to obtain the polystyrene-coated ferriferrous oxide magnetic composite particles. The preparation method has the advantages of simple operation and mild reaction conditions. The obtained magnetic composite particles are evenly dispersed, are stable, and thus have a good application prospect.