X-ray diffraction(XRD), field emission scanning electron microscope(FESEM) and transmission electron microscope(TEM) techniques were used to study the isothermal aging behavior of the metastable β-titanium alloy TB17 after solution treatment in the α+β phase region. The precipitation location, size and morphology of secondary α phase were analyzed. The results show that when aging at 350 ℃, the β→ω phase has taken place, and the ω phase is elliptical in size between 3 nm and 5 nm. When aging at 450 ℃ and 550 ℃, the β→α transformation mainly occurs. The α phase first nucleates and grows at the subgrain boundary and the subgrain defects, and finally forms a fine lamellar α phase, and due to the existence of a large number of subcrystals, the precipitation response time during aging is reduced.