Abstract: The effects of cycle heat treatment at 600 ℃on the microstructure and mechanical properties of TA31 and TC4ELI titanium alloys were investigated by optical microscopy(OM), transmission electron microscopy(TEM), tensile test at room temperature and impact test.The results show that the yield strength and tensile strength of TA31 and TC4ELI slightly increase and the impact toughness decreases significantly after 6 cycles of heat treatment and the variation range of TA31 is larger than that of TC4ELI.As the cyclic times increases to 11, the strength of the two materials decreases slightly, and the impact toughness dose not deteriorate further.Percentage elongation fluctuates in a certain range before and after cyclic heat treatment, and the change is not obvious.No α₂ phase is found in the microstructure characterization.For both TA31 and TC4ELI titanium alloy, during the cyclic heat treatment, the decomposition of the substable β phase and the growth of the thin needle α phase are the main reasons for the performance change of TA31 and TC4ELI.