Abstract: For high-rate plastic deformations of viscoplastic materials, initiation of the adiabatic shear bands (ASB) was generally recognized to result from constitutive destabilizing when the effect of thermal softening overtaking the combined effects of strain hardening and strain-rate hardening. In this paper, the adiabatic shearing of TA2 Titanium alloy was investigated in flat-hat-shaped specimen loaded by split Hopkinson pressure bar. The temperature evolution and in shear deformation zone were measured experimentally by the high-speed-infrared detector. The experimental results show that the initiation temperature is about 470 K which is lower than the recrystallization temperature (about 930 K) evidently. The temperature cannot cause the stress reduce, which means the thermal softening may not the key factor of initiation of adiabatic shear localization; on the contrary, the sharp increase of temperature is the result of high-plastic-strain in adiabatic shear band. The compressive displacement of specimen for ASB initiation descends with loading rate increasing.