Through parallel cores with different permeability contrast, the displacement process of foam flooding after polymer flooding is experimental studied. Using the experiment technology of nuclear magnetic resonance, the fluid distribution in cores with different diameter was studied. The distribution area of bore diameter in which oil is sweepouted of water flooding, polymer flooding and foam flooding under different processes and various heterogeneity conditions. The results show, against water flooding and polymer flooding, the distribution area of bore diameter in which oil is sweepouted is broadened. Foam can plugging the wide aperture in which water and polyer channeling，and foam can sweep the bore diameter which can’t be swept by water and polymer. Foam can not only advance the recovery of low permeability core but also sweep the oil in microbore of high permeability core.