This study investigates the effects of annealing and subsequent deep cryogenic treatment (DCT) on the microstructure and mechanical properties of TC27 titanium alloy. The results show that in the annealed alloy, the α(100) crystal plane grows preferentially along with an increased dislocation density. The size of α-phase significantly increases, forming a basketweave structure between the coarse colony laths. For the ADCT (annealed then DCT) sample, the strongest diffraction peak changes from β(110) after 24 hours of low temperature treatment (ADCT24) to α(101) after 36 hours of low temperature treatment (ADCT36). In the optimized ADCT36 sample, there are more needle-like precipitated α' phases, which result from the β phase supersaturated non-equilibrium densely packed hexagonal lattice formed by non-diffusion transformation of α. The tensile strength and elongation of ADCT36 are 1096.7MPa and 5.6%, respectively, and these improvements are attributed to the homogeneous structure, more isometric and finer secondary α phase, grain rotation, and high-density dislocations.