The hot deformation behavior of Ti-6Al-4V (TC4) titanium alloy was investigated in the temperature range from 650 ℃ to 950 ℃ with the strain rate ranging from 7.7×10-4 s-1 to 7.7×10-2 s-1. The hot tension test results indicate that the flow stress decreases with increasing the deformation temperature and increases with increasing the strain rate. XRD analysis result reveals that only deformation temperature affects the phase constitution. The microstructure evolution under different deformation conditions was characterized by TEM observation. For the deformation of TC4 alloy, the work-hardening is dominant at low temperature, while the dynamic recovery and dynamic re-crystallization assisted softening is dominant at high temperature.