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The TC4 dual-phase titanium alloy was cryogenically treated for different times at -196 ℃ by liquid nitrogen direct cooling, and the grain size was characterized by metallurgical microscope; the volume fraction of α and β phases was measured by scanning electron microscope(SEM); Vickers hardness tester and electronic universal testing machine were applied to characterize hardness and tensile properties respectively. Through the change of grain size and the structure of α phase and β phase, the changes of material hardness and tensile properties were carefully explained. The experimental results show that with the extension of the cryogenic time, the grain size gradually decreases, and the volume fraction of the β phase gradually decreases by transforming into the α phase. After 12 h cryogenic treatment, the crystal grains are obviously refined, and the majority of β phase is transformed to the α phase. The samples shows superior comprehensive mechanical performance. When the cryogenic time exceeds 12 h, the volume fraction of the α phase and β phase have no obvious change. After taken out to room temperature, the recovery effect of the samples cryogenic treated over 12 h was more obvious, and the mean grain size was not significantly refined compared with that of the samples treated for 12 h. Consequently, the strength and hardness of the sample treated over 12 h were slightly lower than those of the sample treated at 12 h. In conclusion, the superior comprehensive mechanical properties can be obtained after cryogenic treated for 12 h in liquid nitrogen. [ABSTRACT FROM AUTHOR]