Vegetable oil-based polyols were prepared from epoxidized soybean oil and methanol by ring-opening reaction. The effects of catalyst dosage, cocatalyst dosage, reaction time, reaction temperature and molar ratio of alcohol to oil on the ring-opening conversion of epoxidized soybean oil were studied under the conditions of tungsten dioxide dichloride (WO2Cl2) as catalyst and silver trifluoromethanesulfonate (AgOTf) as cocatalyst. And the epoxy values of the products were tested. Under the conditions of catalyst dosage 3% (based on the total mass of methanol and epoxidized soybean oil, the same below), AgOTf dosage 4%, reaction temperature 70℃, reaction time 8 h, and the molar ratio of alcohol to oil 28:1, the ring-opening conversion of epoxidized soybean oil was up to 89.13%.The ring-opening product was characterized by IR, 1HNMR, TG and rheological analysis. The TG analysis revealed that the decomposition temperature of polyols was 334℃, higher than that of epoxidized soybean oil (305℃). The rheological analysis showed that the viscosity of epoxidized soybean oil and polyols decreased with the increase of temperature. At low temperature, the viscosity of epoxidized soybean oil polyols was significantly lower than that of epoxidized soybean oil.