Abstract: CT scan technology not only can rebuild the distribution images of microscopic remaining oil in different flooding stages, but also can calculate cores' porosity and oil saturation by CT value that can be converted by X-ray attenuation coefficient, thus realize quantitative characterization of the cores' inhomogeneous and microscopic remaining oil distribution in different flooding stages during the period of each flooding experiment. The conclusion from analysis can be got that these microscopic residual oil can be exchanged quantitatively in different flooding stages.