Dynamic compression tests of Ti6321 titanium alloy were carried out in the temperature range from 193 K to 298 K and strain rate range from 2000 s^-1 to 3000 s^-1 to study the effects of temperature and strain rate on the mechanical properties and deformation behavior of the alloy. The microstructure evolution was observed and analyzed by optical microscope (OM), transmission electron microscope (TEM) and electron backscatter diffraction (EBSD). The results show that with decreasing temperature and increasing strain rate, dynamic yield strength and average flow stress of Ti6321 titanium alloy increase, while the fracture strain decreases obviously. Johnson-Cook constitutive equation is used to predict the mechanical behavior at low temperatures and high strain rates, and the fitting results are in good agreement with the experimental ones. Microstructural study shows that the content of the {112} and {101} extension twins increases significantly as the deformation temperature decreases. The deformation mechanism gradually changes from the auxiliary role of twins to the dominance of twins.