In order to study the influence of thickness on the penetration resistance and failure mode of TC4 titanium alloy plate, the axial symmetry model of blunt projectile impacting plate with different thickness was established using ABAQUS/Explicit finite element software, and numerical simulation of the projectile impact plate with different thickness was carried out.The effectiveness of the simulation model was verified by comparing the results of numerical simulation and impact experiment.The results show that the main failure modes, energy dissipation mechanism and ballistic limit of plate change with the increase of thickness, and there is a critical value for the thickness of the target.For TC4 titanium alloy material, tensile tear failure plays a dominant role in the failure mode of thin plate.And the failure mode of thick plate is dominated by local shear failure.The ballistic limit velocity of plate increases with the increase of the thickness when less than 4 mm or more than 8 mm.When the thickness is between 4 mm and 8 mm, the velocity of ballistic limit basically remains unchanged.