The conventional hydrolyzed polyacrylamide（HPAM）flooding agent has very low viscosity in high temperature and high salinity reservoir. By introducing 2-acrylamido-2-methylpropane sulfonic acid（AMPS）monomer to the PAM backbone，the ultra-high molecular weight（UHMW）terpolymer was synthesized. This is an effective way to improve the temperature resistance and the salt tolerance performance of the polymer. The basic physicochemical properties，rheological properties and oil displacement effect of conventional HPAM and UHMW terpolymer with AMPS monomer were studied.Compared with the conventional HPAM，the effective diameter of UHMW terpolymer was increased by more than 30% at 32 868 mg/L salinity of the simulated water. The molecular chain was more stretched and the network structure were more complete，and the viscosity was more than doubled. Rheological studies show that the thickening coefficient of the UHMW terpolymer shear rheological equation increased by 2 times，and the power-law index decreased by 22%. Therefore，the UHMW terpolymer has higher viscoelasticity，and the tensile viscosity caused by its migration in the formation was more than doubled. The double-sand-filling-tube model experiment shows that the conventional HPAM can only enhance oil recovery by 15.7%，while the UHMW terpolymer can enhance oil recovery by 24.1%. The UHMW terpolymer has better oil displacement effect and has good prospect of application.