Abstract: In order to master the mechanism of hydrogenation improving titanium alloy machinability, microstructure of the hydrogenated Ti-6Al-4V alloy was analyzed by optical microscopy and XRD. Thermal expansion coefficient and thermal conductivity of the alloy were measured by thermal expansion instrument and thermal constant measuring apparatus. Mechanical properties were studied through tensile tests at elevated temperatures. The results show that after hydrogenation β phase ratio increased and δ hydrides formed with increasing the hydrogen content. Compared with the alloy before hydrogenation, thermal expansion coefficient decreased by 6% at 900 ℃ mostly and thermal conductivity increased by 40% at500 ℃ mostly. Tensile strength and elongation of Ti-6Al-4V alloy after hydrogenation decreased by 19% and 74% separately at 800 ℃.