The work aims to optimize the epoxidation process conditions of soybean oil and improve its epoxy value. The concentrated sulfuric acid was used as catalyst to be dissolved in acetic acid and then added into the soybean oil for heating. In the meantime, the hydrogen peroxide was added for epoxidation modification, and the effects of the amount of hydrogen peroxide, acetic acid and concentrated sulfuric acid and reaction temperature on the epoxidation of soybean oil were investigated by testing the acid value and epoxy value. This treatment was contrasted with traditional treatments. When soybean oil was 100 g, 30% (mass fraction) hydrogen peroxide was 80 mL, acetic acid was 9 mL, concentrated sulfuric acid was 5 mL, reaction time was 3 h, and reaction temperature was 60 ℃, the epoxy value of the synthetic soybean oil was the highest (13.27 mol/(100 g)), and the acid value was 0.081 mg/g (in the mass of KOH). The excessively high amount of acetic acid will decrease the epoxy value of the synthetic soybean oil. When the amount of concentrated sulfuric acid is increased, the acid value of the soybean oil will decrease. The epoxy value of soybean oil will increase with the increase of temperature. The epoxy value of the synthetic epoxidized soybean oil conforms to the national standard.