The effect of the important factors on the epoxy value, such as the amounts of hydrogen peroxide and catalyst, the reaction temperature and time, were investigated by the L16（44） orthogonal experiments. The technics were optimized. The results showed that the epoxy value of the product could reach 6.20% with the acid value 1.496 mg NaOH/g and the iodine value 2.58 g/100 g under the conditions of 100 g cottonseed oil, 0.8 g catalyst and 130 mL hydrogen peroxide under 60 ℃ for 7 h. The products were characterized by infrared and nuclear magnetic resonance to confirm that the cottonseed oil was epoxidized to epoxidized cottonseed oil.