Product lifecycle management is one of the main developmental aspects of advanced manufacturing technology. Anti-fatigue design is the key content in product lifecycle management. For designing the fatigue life of shaft exactly and determining the assessment method, the influencing factors must be realized roundly. The mechanical model of shaft is set up at first, and then the main factors that affect the fatigue life of shaft is discussed, the interrelations of the main factors and the framework are founded. The assessment equation of fatigue life for shaft is put forward and the influencing coefficient of multi-axial stress to fatigue life is analyzed. The results of this paper will establish the base of anti-fatigue and assessment life of shaft.