Abstract: There are many production forecast methods at the medium and late stages of waterflooding.However,the pa-rameter value selection is difficult,and calculation is com-plex.A new method for predicting interval oil production is presented in this paper by utilizing interval fluid production and interval water-cut escalating rate.The interval water-cut is achieved through fitting of the actual water-cut esca-lating rate values in Cartesian coordinates.This method is simple and practical.Field application shows that the cal-culation results are reliable.