Novel Ga-based liquid metal (GLM) may be a promising coolant and lubricant in the advanced liquid-metal nuclear reactor, due to its excellent physicochemical properties. But the lubrication and corrosion behaviors of GLM over a wide temperature range are unclear, which are vital to the service safety of the nuclear reactor. In this work, a high-temperature T91 steel was chosen to slide against Al₂O₃ ball in GLM medium and vacuum atmosphere from room temperature (RT) to 800 °C, to clarify this issue. It was found that liquid-metal will decompose and form a Ga-rich film on the contact interface and thus can provide good boundary lubrication at RT and 200 ºC. At 400 ºC, a Ga-rich film also exists and the steel begins to react with GLM to form nano-FeGa₃ crystal, providing the synergistic lubricating effect. At 600 and 800 ºC, GLM corrodes severely the T91 steel and various polymetallic intermetallics are formed, counteracting the lubricity of GLM. In addition, the distinct corrosion mechanisms of GLM on the T91 steel at 600 and 800 °C were preliminary studied and proposed, namely, inside-out growth at 600 °C and outside-in dissolution corrosion at 800 °C.