The influence of pre-strain on phase transformations, microstructures and hardening response in near β Ti alloy Ti-5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe (wt.%) during aging treatment is studied in this work. The results showed that obvious α phase refinement and stronger age hardening effect can be achieved when slightly deformed before aging treatment. Because the intermediate phases (O′, ω and O′′) formation suppressed long-range stress induced martensitic transformation and mechanical twinning, the samples were mainly deformed via dislocations slipping during loading. Numbers of crystal defects were generated during pre-deformation. With the pre-strain increasing, the number density of dislocations increased gradually. These crystal defects generated by pre-deformation would partly annihilate upon early aging, but the precipitation of α was also be promoted and resulted in refined α precipitates. In the sample pre-strained to 5 %, the average thickness of α precipitates was decreased by 57 % during aging at 600 oC than the unstrained sample, and the number density was increased from 7.0±1 laths/μm2 to 22.0±3 laths/μm2. Some platelet-shaped α were formed when the samples experienced comparably large pre-strains, i.e. 12 % and 20 %. It proved clearly that the refined α precipitates and higher hardening effect could be obtained by pre-deformation plus aging treatment in titanium alloy.