Abstract: High temperature tensile experiments were earned out to investigate the effect of hydrogen on the superplastic deformation behavior of Ti-6Al-4V titanium alloy. The influence of hydrogen on the microstructure evolution of the alloy was analyzed by OM, SEM, TEM, and XRD. The results show that the amount of 13 phase in the hydrogenated alloy increases with increasing hydrogen content, and martensite begins to form while the mass content of hydrogen reaches to 0.2% and becomes coarser with the increase in hydrogen content. A reasonable hydrogen content can improve the superplastic behavior such as increasing the m value and lowering the flow stress and temperature. The addition of 0.1% hydrogen in Ti-6Al-4V alloy ean result in a decrease in peak flow stress of 53% and a decrease in deformation temperature of 6012. Due to addition of hydrogen the dislocation density of the hydrogenated alloy after deformation is lower than that of the unhydrogenated alloy.