Abstract: The surface of 321 stainless steel was treated by aluminizing process, and the effect of aluminized layer on the low-cycle fatigue property and fracture mechanism of 321 stainless steel was investigated. Results demonstrate that for the same strain amplitude, the fatigue life of aluminized 321 stainless steel is obviously lower than that of as-received sample. The fatigue crack tends to originate in the Al₂O₃ thin film and at the interface between matrix and aluminized layer, which propagates along the grain boundary of FeAl phase. Meanwhile, the Fe₃Al with DO₃ structure may transform to the FeAl with B₂ structure, reducing the strength of aluminized steel. Besides, the sigma phase, deposited in the process of aluminizing, further accelerates the crack propagation, resulting in reduced fatigue life of aluminized 321 stainless steel.