Abstract: Calculation of oil saturation with current numerical simulation method has the disadvantages that the amount of calculation is large and calculation period is long, thus it is not suitable for rapid evaluation of remaining oil saturation distribution of oil layers. In order to solve this problem, a simple and easy method is presented to rapidly evaluate the distribution of remaining oil in waterflooding oilfield. It calculates oil saturation through analyzing areal distribution of water saturation around water injectors. This method is applied in calculation of the remaining oil saturation of the upper 1-1 layer in unit Ⅷ in Shuanghe oilfield. The calculation results are basically in accord with the numerical simulation results.