Abstract: In order to investigate the effect of double heat treatment on the microstructure evolution of TA15 titanium alloy, the change of α phase content for TA15 alloy by controlling the heating temperatures and holding time during the first and the second steps of heat treatment were analyzed, and the microstructure and hardness of the alloys were characterized by using optical microscope and Vickers hardness tester, respectively. The results show that the content of equiaxed α phase gradually increases with the increase of the heat treatment temperature and holding time in the first step of heat treatment, and the hardness of the alloy also increases. The content of equiaxed α phase is the main factor affecting the hardness value of TA15 alloy of this time. With the increase of temperature and holding time during the second step of heat treatment, the contents of equiaxed α phase for TA15 alloy are all higher than 40%, resulting in the formation of the equiaxed structure of TA15 alloy.However, the equiaxed α phase content is not the main factor of hardness at this time.