Abstract: The methacrylate ester - diisooctyl maleate - styrene terpolymer was synthesized through esterification and polymerization using methacrylic acid, high carbon alcohol and maleic acid isooctyl ester and styrene as raw materials, toluene as solvent, and p-toluene sulfonic acid as catalyst. The synthesis conditions and pour point depressing performance of the terpolymer was studied. The results show that the terpolymer, synthesized at the conditions of molar ratio of monomers of 5:1:1, initiator of 0.8% and 105 ℃, 5 h, has the best pour pint depressing performance. The pour point of the 150SN base oil decreases 22 ℃ when the dosage of depressant is 1.0%.