A method which applies step perforation to improve the effect of polymer flooding is presented against the problems of poor producing degree of low permeability, remaining oil in the inner thick oil layer abounds, and uneven vertical producing degree. After water flooding, the thick layers are perforated selectively followed by water flooding potential tapping, and the polymer flooding is performed ultimately. By carrying out laboratory physical oil displacement experiment of three tube parallel cores and applying theoretical formulas, reasonable polymer injection parameters are determined and the impacts of polymer flooding after step perforation on development effectiveness are also studied. The results showed that the better effect of polymer flooding was obtained by using big pre slug, high molecular weight polymer, and echelon descending concentration slug combinations. And projects which had adopted step perforation showed a bigger producing degree on low permeability layers and a better effectiveness on polymer flooding compared to the ones not adopted step perforation. The ultimate recovery was increased by 1.28%.