Abstract: The modified Mg-13Gd-4Y-2Zn-0.5Zr alloy was aged. The effects of different aging time and working temperature（test temperature） on microstructure and hardness of the alloy were investigated. The results show that the optimum aging time is 12 h and the maximum hardness is 128 HV at 225 ℃. When the working temperature changes, its hardness reaches the peak aging time is the same. When the working temperature is below the aging temperature, the high temperature hardness of the alloy has better stability and only decreases 4-9 HV. When the working temperature exceeds the aging temperature, the high temperature hardness of the alloy decreases obviously, and the reduction is about 24-30 HV.