The surface active polymer PAS with low relative molecular weight was prepared by free radical polymerization of surfactant monomer N- (hexadecyl) -N- (sulfonyl) acrylamide and acrylamide. The structure of PAS was characterized by FTIR, and the related properties of PAS as an oil displacement agent such as viscosity increase, emulsification, injection and enhanced oil recovery were studied. At 45 ℃ and 2410 mg/L, the viscosity of PAS solution at 1000 mg/L is 32.6 mPa. s, which is higher than partially hydrolyzed polyacrylamide (18.9 mPa. s) with the same relative molecular weight. Under the condition of PAS concentration of 1000 mg/L, the water dissolution rate of the emulsion formed with crude oil is 5% for 120 min, and the viscosity retention rate of three adsorption is 114.11%, which still has good emulsification after adsorption. When the core permeability is 0.025 μm2 and the stable pressure is 1.02 MPa and the core permeability is 0.1 μm2, the PAS flooding can improve the oil recovery by 19.02% on the basis of water flooding, which is 5% higher than partially hydrolyzed polyacrylamide flooding and comparable to the enhanced oil recovery of polyacrylamide-sodium carbonate - sodium petroleum sulfonate system, only 0.58% lower.