Abstract: In viewing of the problems existing in prediction offluid production when designing large pump replacement program, a concept of critical flow pressure is introduced according to the real situations of production. When predicting production, values of the selected flow pressures should not be lower than the corresponding critical flow pressure of each block. The erroneous ideal, i. e. the lower the flow pressure is, the higher the production will be, is corrected and the predicted results are closer to the real production.