Abstract: Fatigue experiments for bcc near-β Ti alloy were carried out under the conditions of different strains and cycles, and the plastic strain mechanism during cycle was analyzed. Internal relation between cyclic deformation characteristic and surface slid mode was analyzed by studying the effects of slip mode, microstructure evolution on early micro-cracks initiation and observing dislocation configuration before and after fatigue testing. The results show that typical planar slip characteristic and surface stress concentration appeared in near-β Ti alloy after compressive cyclic deformation. The stress-localized slip bands as well as the planar slip mechanism were induced by the dislocation annihilation, detwinning progress, and the simplified microstructure upon the stress cycling.