Fatigue　failure　mechanism　of　Ti60　titanium　alloy　under　tension–torsion　multiaxial　loading　in　the　very　high　cycle　regime　was　studied　first,　and　the　results　showed　that　the　shear/axial　stress　ratio　directly　affects　the　failure　mechanism.　When　the　shear/axial　stress　ratio　is　relatively　small,　cracks　tend　to　originate　from　the　subsurface　in　single-point　initiation　mode,　and　the　larger　the　shear/axial　stress　ratio,　the　more　cracks　tend　to　originate　from　the　surface　in　multi-point　initiation　mode.　Then,　a　pragmatic　equivalent　method　for　multiaxial　to　uniaxial　load　based　on　the　law　of　shear/axial　stress　ratio　on　fatigue　strength　was　proposed.　Based　on　this　method　and　uniaxial　S-N　curve,　the　fatigue　lives　of　Ti60　specimens　under　shear/axial　stress　ratios　of　1.37,　1.95,　and　3.53　was　predicted,　and　the　experimental　results　showed　that　the　prediction　error　is　basically　within　a　factor　of　3.　©　2024