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Quantitative analysis on the deformation mechanisms of a rotationally accelerated shot peening (RASP) processed gradient structured Ti was studied by using electron back-scattering diffraction technique. A 2000 μm thick gradient structure was introduced from the strain-free center to the treated surface. The low angle grain boundary fraction evolution showed that, with decreasing distance from the surface, dislocation generated continuously in the core region, then became saturated in the twin transition region, and finally decreased in the nano-structured region. Three twinning systems were identified: 11 2¯ 1, 10 1¯ 2 extension twin (ET) and 11 2¯ 2 compression twin (CT). The volume fraction of 10 1¯ 2 ET increased firstly and then decreased when approached to the surface, while 11 2¯ 2 CT showed an opposite tendency. The volume fraction of 11 2¯ 1 ET decreased gradually form the center to the surface …