In this paper, the dynamic mechanical properties and sensitivity of adiabatic shear banding of TC21 alloy was investigated. The lamellar microstructures with different thicknesses of lamellar α were obtained via different heat treatments. The dynamic compression properties and sensitivity of adiabatic shear banding behavior of TC21 alloys having lamellar microstructures were tested on the Split Hopkinson Pressure Bar. The results showed that the thickness of lamellar α increased from 0.57μm to 6.49μm with the decreasing of the cooling rate. Under dynamic compression experiments, the dynamic strength decreased as the thickness of lamellar α increased; while the dynamic strain exhibited an opposite trend. Under forced shearing experiments, on the one hand, the sensitivity of adiabatic shear banding increased with the decreasing of the thickness of lamellar α at the same impact velocity; on the other hand, the sensitivity of adiabatic shear banding increased for the same microstructure with the increasing of impact velocity.