Ga-based liquid metals have promising applications as coolants and lubricants in the computer science, medical, and nuclear industries. In this paper, soft metal Cu was used as an additive to improve the lubricating performance of Ga-In-Sn. CuGa2 phases were in-situ generated. At room temperature (RT, 25°C) and 150°C, GC0.2 and GC0.5 (Ga-In-Sn doped with 2   wt.% and 5   wt.% Cu) exhibited significantly better lubricating properties than Ga-In-Sn. At 150°C, the wear rate of T91 steel lubricated by GC0.2 was 72.95% lower than that lubricated by Ga-In-Sn. At 300°C, GC0.2 maintained a similar lubricating performance to that of Ga-In-Sn. The lubrication mechanism showed that the change in lubricant characteristics and friction film were the main factors to improve the lubricity.