The mechanism of overall residual oil saturation reduction by polymerflood in heterogeneous porous media is studied. A compositional chemical flooding simulator (UTCHEM) using high resolution numerical method was used to simulate the previous coreflooding experiments as well as to study the sensitivity of different parameters -heterogeneity, capillary pressure, mobility ratio, etc., to the oil recovery and residual oil saturation. To provide the important data for the numerical simulation, a porous plate experiment was conducted to construct capillary pressure curves from the capillary pressure measurement data of the target porous media -Antolini sandstone outcrops. A capillary pressure measurement device was designed and made capable of desaturating four sandstone samples simultaneously with the realistic reservoir fluids and reservoir temperature. The study showed that polymerflood reduces the overall residual oil saturation in heterogeneous porous media by mitigating the negative impact of heterogeneity present in the media.