Abstract: The fatigue life of Ti6321 alloy with phase differences of 0°and 30°is analyzed by tensile-torsional fatigue test. The propagation path of micro-cracks and macro-cracks at 0°phase difference is studied, and the fatigue fracture surface analyzed.Resultsshow that axial-torsional fatigue life of Ti6321 alloy at 30° phase difference is shorter than that at 0° phase difference. The Ti6321 surface micro-cracks, mainly affected by shear stress, is initiated in the range of 20°~30° to axial direction. Besides, with the increase of equivalent stress amplitude, the number of initiated surface micro-cracks increases. And the main crack tip makes a sharp turn in the direction of small angle to axial direction due to the main crack and merges with micro-cracks during propagation, which restrains the main crack propagation along the maximum normal stress direction. The main axial-torsional fatigue crack, influenced by the micro-cracks, presents step morphology in the propagation zone.