Abstract: The water displacement efficiency is an important parameter for characterization of reservoir displacement capability. Traditionally, short core is used in the displacement experiment to calibrate the water displacement efficiency, and further evaluate the reservoir development potential. However, this method is not suitable in Wenchang 13-2 Oilfield because the present reserve recovery of 56.8% in the second oil zones of this field has exceeded the displacement efficiency of 47.08% previously calculated by the experiment with short core in the early years. This indicates that the traditional calibration method is not reasonable for Wenchang 13-2 Oilfield, and it is necessary to re-determine the water displacement efficiency of Wenchang 13-2 Oilfield. Based on the fractal dimension relative permeability curve, production log, and saturation test and water displacement efficiency with long core experiment, the authors conducted the study of the water displacement efficiency in the second oil zones of this field. It indicates that the parameter of displacement experiment with long core is more suitable for calibrating the water displacement efficiency of water flooded sandstone reservoir of Wenchang 13-2 Oilfield. The update water displacement efficiency 84.27%, brought a new understanding about the water displacement efficiency. Also, its application in the numerical reservoir simulation results in great improving in the estimation of the residual oil, and can be used to guide the adjustment and tapping potentials of the oil field in later stage.