Ga-based liquid metal may be a novel coolant and lubricant for the steels at high temperature and extreme pressure in the nuclear reactor. It is recently reported that the formation of FeGa₃ film may be responsible for the good lubricity of liquid metal, but no proof can clarify this point and its wear behavior is unclear. Therefore, an in-situ FeGa₃ film was prepared through the hot-reaction between liquid Ga₆₅In₂₂Sn₁₃ (65% Ga, 22% In, 13% Sn by mass) and T91 steel at 600 °C in this paper. The results indicate that FeGa₃ film forms and bonds strongly to the steel surface. It has good mechanical and tribological properties at room temperature, but increases the wear at 600 °C. The finding provides the technical support for the safety service of the steels in the liquid-metal environment and is also a new strategy for protecting the steel.