Dynamic shearing experiment has been done for TC6 titanium alloy by using the technology of split Hopkinson bar. The formation mechanics of adiabatic shear band of TC6 titanium alloy have been studied by optical microscope (OP), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is shown that the formation mechanics of adiabatic shear band are different due to the different microstructures for the TC6 titanium alloy. To the spherical equiaxed microstructures, its formation of shear band is due to the multiplication, moving and clogging of dislocation; and to the lamellar microstructures, the formation of shear band is due to the dynamic recrystallization.