The Mg-6Gd-3Y-0.5Zr magnesium alloy had been used in aerospace structural products，its internal damping performance was directly related to the dynamic characteristics and response of structures，the internal damping performance of Mg-6Gd-3Y-0.5Zr magnesium alloy was studied using DMA tester and the mechanism was analyzed.The results show that the damping of Mg-6Gd-3Y-0.5Zr alloy gradually increases with the increase of strain amplitude and the mechanism at temperature conforms to the G-L dislocation damping theory.The damping performance of alloy gradually increases with the increase of temperature.Within the tested frequency range of 1~80 Hz，the lower the frequency is， the more sensitive the damping is to the change of temperature，and the influence of temperature on damping performance conforms to the Schoeck theory.