Abstract: By means of optical microscopy (OM), scanning electron microscopy (SEM) and tensile testing machine the influences of heat treatment process on microstructure and tensile property of Ti55531 titanium alloy were studied. The results show that with the increase of solid solution temperature (790-810 ℃), the content of primary α phase in the alloy decreased, the strength increased and the plasticity decreased. With the increase of aging temperature (500-600 ℃), the secondary α phase in the alloy coarsened, the strength of alloy decreased and plasticity increased. When the prolongation of aging time (2-8 h) at 550 ℃, the content of secondary α phase in the alloy increased, the strength of the alloy increased and the plasticity decreased.