An anti-fatigued criterion of annularly breached shaft on mechanical design has been put forward, and the main factors that affect fatigue life of shaft are discussed. The interrelation of the main factors and the framework is founded. A new assessment method to fatigue life of shaft has been put forward according to Corten-Dolan’s theory modified Miner's rule. The effect of supporting conditions to fatigue life of shaft is discussed and the influencing parameters are obtained. The results show that the fatigue life of broad support in two sides is longer than that of narrow support in two sides. The results will establish the base of anti-fatigue design of shaft.