Isothermal hot compression tests of a Ti600 alloy after hydrogenation were carried out over the temperature range of 760 to 880℃ and strain rate range of 0.01 to 10 s-1. The influence of hydrogen content was studied on the flow stress and activation energy of deformation. The microstructural changes were examined by transmission electron microscopy (TEM). The results show that the addition of 0.3% hydrogen in Ti600 alloy can decrease the hot deformation temperature by 80 ◦C and increase the deformation strain rate by two orders of magnitude. Both the flow stress and activation energy of deformation of Ti600 alloy decrease gradually with increasing hydrogen content in the hydrogen range of 0 to 0.3%. TEM observation suggests that dynamic recrystallization (DRX) is promoted after hydrogenation. Hydrides δ (fcc structure) exist in the specimens with 0.3% and 0.5% hydrogen, and the hydrides tend to be broken up and twisted with increasing hydrogen content after deformation. The mechanism of hydrogen reduced flow stress of Ti600 alloy has been discussed in detail.