With the raw material maleic anhydride, mixed alcohols and styrene, the copolymer maleic anhydride mixed alcohols ester- styrene(PMST) is synthetized, the reaction conditions are investigated and the pour point depressant effect is tested. The suitable esterifications are, molar ratio of mixed alcohols and material maleic anhydride is 2:1, esterification time is 3h, amount of catalyst is 1.5%, amount of esterification solvent is 20%; and the suitable polymerizations are, molar ratio of styrene and maleic anhydride mixed alcohols is 1:1, amount of polymerization solvent is 50%, polymerization temperature is 80℃, amount of initiator is 1.5%, polymerization time is 3h. IR and 1H-NMR spectra confirm the structure of products. When the addition dose of PMST is 0.4%(based on the mass of wax oil), and the heat treatment temperature is 70℃, PMST can make the pour point of wax oil used in experiment decline 26℃,this pour point point can make high freezing point wax oil have an ideal fluidity in room temperature even lower temperature.