Ti-20Al-22Nb (at%) alloys were prepared by investment casting. The microstructures and tensile properties at room temperature of as-cast, hot isostatic pressing and annealed alloys were analyzed. The results show that solidified alloy has course widmanstatten structure, which consists with β matrix, fine acicular α2 phase and a small amount of O phase. The phase transformation inside original β/B2 grain was incomplete owing to non-equilibrium solidification. The loose defect and inhomogeneity of microstructures causes low plasticity of the material. The porous defects are eliminated by hot isostatic pressing in the two-phase region ofα2+β/B2. , peritectoid reaction of β/B2+α2→O promotes the formation of ring O phase around strip α2 phase, and β phase path through a process of equilibrium state transportation. The elongation of the alloy increases from 2% to 5%. Increase to 11%.