The life prediction of the pump and the counting method of stress were the subjects of this investigation. Aiming at the defect of the previous consideration that failed in attempts to count stress cycles, the concept of critical net stress was proposed to modify the counting principle. The improvements were made based on the concept of critical net stress. The improved counting method for predicting the fatigue life of an axial flow pump impeller was implemented. In addition, the key steps of the fatigue life prediction method were introduced based on 2-D probabilistic Miner-rule. 