High-pressure torsion (HPT) processing under a pressure of 6.0 GPa was applied to Ti29.7Ni50.3Hf20 (at.％)alloy.Two types of structure were observed after HPT with 3 revolutions:first one is the mixture of amorphous phase and retained nanocrystalline;second is the alternating bands of amorphous phase and high defect density crystalline.As a result,post deformation annealing (PDA) at 500-700 ℃ leads to the non-uniform distribution of martensite and parent phase grains.The grains of martensite are twice larger compared to that of parent phase.The nanocrystalline and ultrafine grains form after annealing at 500-600 ℃ and 700 ℃,respectively.The twinning mechanism does not change with the reduction of martensitic grains up to ～35 nm.The relationship between strength and grain size in Ti29.7Ni50.3Hf20 alloy obeys the classical Hall-Petch relationship with a coefficient of 10.80 ± 0.39 GPa nm1/2.