A damping measurement system was developed for high temperature materials using double-reed cantilever specimens by means of resonant-dwell under base excitation in a high-temperature and vacuum environment. Some methods were proposed to improve the accuracy of damping measurement. The effect of air damping on damping tested results was analyzed. The damping of Ti-6-4 alloy was tested by the system and the relationships of material damping to temperature, strain amplitude and vibration frequency were studied. Results show that air damping has a significant effect on the damping of materials. The damping of Ti-6-4 alloy keeps constant and the vibration frequency has little effect on it below 400 oC. However, it increases rapidly with temperature elevation above 400 oC and the vibration frequency has a complicated effect on it. The effect of strain amplitude on the damping of Ti-6-4 alloy can be neglected in the temperature range from 25 to 600 oC