Abstract: Good application results of field polymer flooding test have been achieved in many oil fields, but “profile reversion” often occurs during polymer flooding process and the conventional theory of alternate polymer injection to control profile reversion is not suitable for vertically heterogeneous reservoir development. Starting with resistivity calculation of oil-water two-phase flows, this paper studies the profile reversion mechanism and its discriminant method, discusses the EOR mechanism of alternate polymer injection during general oilfield development and determines the limits of permeability contrast applicable for polymer flooding. The study result shows that the injection volume corresponding to the extreme points of fluidity in each layer is just the point where the injection profile reversion occurs during polymer flooding; when the vertically heterogeneous reservoirs are developed generally, liquid absorption amounts in low-permeability layers are not significantly improved by alternate polymer injection, whereas the processes of oil aggregation and oil bank forming can enhance oil recovery; when the permeability contrast is higher than 4 in the vertically heterogeneous reservoirs, the single-stage polymer flooding can’t get the optimal development effect, the injection profile should be modified and then polymer flooding can be carried out again to improve the oil recovery percent of reserves.