Abstract: In order to improve oil displacement efficiency by polymer flooding further,performance of polymer with relative molecular mass above 35 million was assessed,and the structure of ultra high molecular weight polymer solution was observed.Under test conditions of 70 ℃ and salinity of 11 200 mg/L,the viscosifying ability,temperature tolerance,salt tolerance,shear rheology and viscoelasticity of ultra high molecular weight were evaluated,and compared the performance of ultra high molecular weight polymer with that of common polymer.The displacement efficiency of two polymers was analyzed by using physical simulation experiment,and the microstructure of the two kinds of polymers was observed through CRYO-SEM.The results show that ultra high molecular weight polymer can form a more compacted network structure aqueous solution,its viscosifying and salt tolerance ability are 30% higher than that of common polymer,temperature tolerance 40% higher,burg number is twice that of the common polymer,oil recovery 6.5% higher than common polymer displacement.It has proved that ultra high molecular weight polymer is very good agent for displacement of oil.