In process of polymer flooding，the phenomenon of profile reversal has bad influence on enhancement of oil recovery. In order to further improve effect of polymer flooding，we make some researches on the effect of polymer flooding，the reversal time of polymer profile and its influencing factors through the methods of theoretical analysis and laboratory test. Results showed that with the increase of the core permeability，reversal time of polymer flooding profile would delay and the delay degree would increase. When the concentration of polymer solution was 1600 mg/L，permeability differential was 4 and the core permeability was more than 1200×10^-3μm²，this phenomenon became especially obvious. With the increase of permeability differential and thickness ratio of divided layer （high permeability layer /low permeability layer），that was to say，with the increase of formation coefficient differential，the reversal time of polymer flooding profile was advanced. When the concentration of polymer solution was 1600 mg/L，average core permeability was 300×10^-3 μm² and formation coefficient was 10，the reversal time of polymer flooding profile was advanced to 0.06—0.07 PV. With the increase of core permeability and formation capacity differential，the enhancement of oil recovery increased at first and then decreased. The reversal time of polymer flooding T_p and formation capacity differential D_j satisfy the equation T_p=a（D_j-1）^-1( here，a was the reversal coefficient），With the increase of the polymer solution concentration，the reversal coefficient decreased，profile reversal time was advanced. Using this equation，the relationship between profile reversal time and formation coefficient differential could be quantitative described，and the injection parameters could be adjusted timely and the effect of polymer flooding could be improved.