The microstructure characteristics and fracture mechanisms of Ti-6Al-4V-0.55Fe(TC4F) alloy with bimodal structure under low cycle fatigue and dwell fatigue at room temperature were investigated in this paper. The stress-strain behavior of the alloy was analysed for low cycle fatigue with a total strain amplitude of Δε t /2=1.20% and dwell time of 0.05, 10, 20 and 30 s, and the microstructure evolution of the alloy after fatigue deformation was also investigated. The results show that the difference in the crystallographic orientation of adjacent grains has an important effect on fatigue crack initiation in the TC4F alloy. On the one hand, whether at the α/α phase boundary or the α/β phase boundary, the greater the difference in grain orientation, the more likely it is that cracks will initiate; on the other hand, twinning within the α phase leads to a greater difference in orientation between the adjacent grains of the twinning boundary, which can lead to the formation of cracks within the α phase. As the fatigue dwell time increases, it leads to the activation of more prismatic slip systems in the α phase and the dislocation slip causes stress concentration at the phase boundary, which in turn leads to a reduction in fatigue life. Finally, the fatigue crack propagation mode is discussed for different dwell time.