Effects of hydrogen on superplastic deformation behavior were investigated through high temperature tensile experiment in this paper. It is found that reasonable hydrogen contents can improve the superplastic behavior such as lowering flow stress and temperature and increasing m value. While addition of 0.1wt% hydrogen in Ti-6Al-4V alloy, peak flow stress decrease to 53%, deformation temperature decrease 60°C. The influence of hydrogen on microstructure transition by means of optic microscope, SEM, TEM and XRD was also researched. The results show that β phase amounts in the hydrogenated alloy increase with hydrogen contents, while hydrogen contents reach to 0.2wt%, martensite becoming coarser with the increase of hydrogen contents. Moreover, dislocations density of hydrogenated alloy after deformation is lower than that of unhydrogenated alloy because of hydrogen action.