Abstract:TC4 titanium alloy plates were impacted by projectile at a high speed. The microstructure changes inside and nearby the adiabatic shear bands (ASBs) were observed by transmission electron microscope (TEM). The microstructure nearby the ASBs indicated that the boundaries of the ASBs might be the sources for the crack initiation. High stress was concentrated nearby the ASBs, making it easy to form high density dislocation configurations (such as tangled dislocations, banded dislocation cells and so on) and stress induced martensite. The microstructure inside the ASBs indicated that they were mainly induced by high stress. Along the direction vertical to the ASBs, the closer to the center of the ASBs, the more serious the grain fragmentation is. The typical characteristics of dynamic recrystallization (DRX) were not found in the ASBs, thus the present observations did not support the traditional viewpoints that DRX occurred in the ASBs and the origin and dissemination of the ASBs were related to the DRX. Besides, amorphous was also found in the center of the ASBs.