In order to develop a multifunctional oil additive with corrosion inhibition and viscosity reduction，poly methyl acrylate-acrylic acid imidazoline（MA-ACI）was synthesized using methyl acrylate and acrylic imidazoline as raw materials， and characterized by FT-IR and gel permeation chromatography（GPC） . The corrosion inhibition property of MA-ACI was evaluated by rotating hanging plate method and electrochemical Tafel polarization curve method， and its viscosity reduction property was sdudied by rotating viscometer. The results showed that MA-ACI with the relative molecular weight 36582 could be obtained under the condition of 8∶1 molar ratio of methyl acrylate to acrylic imidazoline， 1% initiator AIBN， 80℃ reaction temperature and 10 h reaction time. MA-ACI had good corrosion inhibition effect on N80 steel sheet， and had good viscosity reducing effect on crude oil of Wei5-57 well in Jiangsu oilfield. At 30℃， the inhibition rate measuring by rotating hanging plate method was 82.06% with MA-ACI dosage of 0.10 g/L， and that measuring by electrochemical polarization curve method was 90.21% with MA-ACI dosage of 0.40 g/L. The viscosity reduction rate of crude oil of Wei5-57 well in Jiangsu oilfield was 85.28% under the condition of 100 μg/g MA-ACI and 70℃