To enhance oil recovery in Saertu oilfield of Daqing，an experimental study of polymer flooding was performed in a layered heterogeneous reservoir model with different molecular weight polymer using CT scan imagery technology. The layered heterogeneous model consists of three connected sandstone layers of equal thickness. Special core holder was designed for CT scanning. CT scanning technology was applied to tracing the development of the saturation profile of the layered model during polymer flooding process，which can quantitatively characterize the oil saturation distribution. Enhanced oil recovery and remaining oil distribution in each layer were analyzed during the process of water flooding and polymer flooding. Oil recoveries of group DQZ3 and group DQZF1 are up to 77.3% and 72.2% respectively by polymer flooding，which have increased by 39.4% and 21.9% each compared with water flooding. Average water saturation of group DQZ3 and group DQZF1 in the high permeability layers is improved by 4.1% and 2.7% respectively after polymer flooding. Experimental results show that the polymer flooding may effectively sweep the remaining oil in the middle-to-low permeability layers after water flooding，and also reduce the residual oil saturation of the high permeability layers that has very low residual oil saturation after water flooding. Oil recovery would be enhanced as the polymer molecular weight increases.