Methoxy polyethylene glycol methacrylate-styrene polymer was synthesised with phosphotungstic acid supported on silica(PW12/SiO2),this catalyst was prepared by putting tungstophosphoric acid into the three dimensional structure of silica. The optimized condition for the esterification were determined with orthogonal experiments as:molar ratio of methoxy polyethylene glycol to methacrylic acid was 1:3,amount of catalyst was 1%，amount of inhibitor was 1%,reaction time was 10h, the esterification rate could reach to 93.6% and the yied was up to 83.46%.Under high loading amount, phosphotungstic acid has a great degree of dispersion on silica,and without surface packing of bulk phosphotungstic acid.The catalyst has a low desorption on the reaction and still has a excellent catalytic effect after using many times.