Abstract: Because water cut is an important index to reflect production performance of water?flooding oilfields, water cut forecasting based on available production data is a very meaningful work. Conventional methods for it are hard to be used to establish relationships between the changes of water cut and production time, and solving the parameters in conventional models are relatively complicated. On the basis of a growth curve model for field development index forecasting, a new model is established to forecast water cut changes with production time . The new model is characteristic of simple expressions, easily getting parameters and more accurate prediction. Case studies from 2 reservoirs show that the forecast results obtained by the model are more accordant with the actual production performances, and the new model is more practical