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Fatigue experiments with funneled-shape specimens of 2A12-T4 aluminumalloy were carried out to study the multi-axial high-cycle fatigue failure behavior undertorsion loading. The torsion S-N curves under different mean shear stress were obtained,including mean shear stressτm=0MPa,25MPa,50MPa,75MPa,100MPa. Experimentresults showed fatigue life under the same shear stress amplitude reduced graduallywith the increase of mean shear stress. However, the reduction of fatigue life whenmean shear stressτm=75MPa andτm=100MPa was not obvious. The micro analysis ofspecimen fracture appearance was conducted in order to obtain the fracturecharacteristics under torsion fatigue loading. Fatigue crack initiated in specimensurface and there are clear source region, extension region and final region in thefracture appearance. Obvious abrasion mark appeared and thermal oxidationphenomenon took place due to reversed torsion.