Both the phase and microstructure evolution of MIM Ti-6Al-4V alloy in the thermo-hydrogenation treatment process were investigated, especially the effect of hydrogen content, to improve mechanical properties. The results show that β-Ti becomes more and more initially and then δ titanium hydride is precipitated as hydrogen content in the alloy increases during the hydrogenation process at 650 °C, so that the bulky sheets in the microstructure of as-MIMed alloy are gradually broken into tiny needles. Solution treatment at 850 °C and isothermal aging at 620 °C make the dissolved hydrogen in the alloy distribute more uniformly and let more needle-like δ precipitate. The alloy remains a refined needle-like microstructure after vacuum dehydrogenation at 720 °C, and the higher the dissolved hydrogen content in the hydrogenised alloy, the more the refined needle-like microstructure after dehydrogenation. For the alloy with 0.51wt% H after hydrogenation, its ultimate tensile strength, yield strength and elongation after dehydrogenation are increased by 11%, 13% and 19%, respectively, in comparison with those of MIM Ti-6Al-4V