The mechanism of fatigue crack propagation of γ-TiAl alloy under different strain ratios is studied using the molecular dynamics method. The results show that fatigue crack propagates in the manner of cleavage firstly, and then propagates through disordered region by driving force. Finally, it changes into sub-main crack mechanisms. The difference is that the change in the mode of crack propagation occurs at different times under different strain ratios. At the stage of plastic deformation, dislocations emit at different times and glide at different planes due to different strain ratios. Defects, such as vacancies, divacancies, trivacancies, etc are generated during dislocation gliding. Meanwhile stacking faults are generated along the different close-packed planes under different strain ratios.