Abstract: Based on John-Cook constitutive model and damage model, the two-dimensional model of split Hopkinson pressure bar system was established by Lsdyna software. The adiabatic shear process of TC4 titanium alloy hat-shaped sample was simulated. Stresses, plastic strains and temperatures of the localized deformation area were studied and compared with test results. The adiabatic shear mechanism of TC4 titanium alloy was discussed. The results show that at the impact velocity of 13 m·s^-1, localized deformation phenomenon was obviously observed in the TC4 titanium alloy hat-shaped sample; the maximum stress in the localized deformation area was 1 530 MPa obtained by simulation and the fracture limit plastic strain was 0.205, and the maximum temperature was 344.3 K. The region with relatively high equivalent plastic strain and the region with relatively high temperature in the localized deformation area had vortex distribution feature, and the location of the two regions was the same; the adiabatic shear band was formed in this region. The simulated true stress-true strain curve of the hat-shaped sample and the formation location of the adiabatic shear band were both in good agreement with the test results, which verified the accuracy of the simulation. The adiabatic shear band structure of TC4 titanium alloy was obvious isometric crystal structure, and there was a clear dividing line between adiabatic shear band structure and α matrix structure.