The acrylate was synthesized though direct esterification firstly with PPG-400 and acrylic acid. And then an oil-soluble quadripolymer was synthesized by solution polymerization with octadecyl acrylate, styrene, acrylamide and the prepared acrylate. The chemical structure and composition of the copolymer was identified by IR spectrum and NMR. The optimum reaction conditions were obtained as follows : n(octadecyl acrylate): n(acrylamide): n(styrene): n(acrylate)= 6:1:2:1, with the initiator dosage being 1%, polymerization temperature being 80℃, and the reaction time being 6 hours. Further，the viscosity was decreased from 3008mPa.s to 895mPa.s when the dosage of viscosity reducer was 1000mg/L at 50℃.