ZrO2/Fe3O4 carrier was prepared by the method of co-precipitation and SO42- was loaded successfully as the active center by dipping. The composition, structure, surface acidity and magnetic properties of the catalyst were characterized by FT-IR, EDS, XRD, etc. The magnetic solid acid catalyst was applied to the preparation of polyols from the ring-opening of epoxy soybean oil by glycerinum.The effects of catalyst dosage, temperature and reaction time on the ring-opening conversion and hydroxyl value of the product were investigated. The experimental results showed that the best reaction conditions were when the catalyst dosage is 1% of the mass of epoxy soybean oil, the reaction temperature is 80℃, and the reaction time is 6h. Under this condition, the ring-open conversion is more than 99%, and the hydroxyl value of the product is 365mgKOH/g.