The invention relates to a method for preparing a CuGa2 thin film on the curved surface of a copper-based metal material through gallium-based liquid metal. The method comprises the steps that metal gallium, metal indium and metal tin are added into a crucible according to a certain mass ratio, heated and stirred to obtain the gallium-based liquid metal with the melting point as 5-20 DEG C, the gallium-based liquid metal is added into aqueous alkali for removing an oxide of the surface, and then a copper-based metal workpiece is put into the aqueous alkali and is in contact with the gallium-based liquid metal; aluminum foil is used for being in contact with the surface of copper-based metal for an electrochemistry reaction to generate voltage, the gallium-based liquid metal is induced to be quickly spread on the surface of the copper-based metal workpiece, and finally the CuGa2 thin film is obtained. The method for performing quick film coating on the curved surface of the copper-basedmetal is achieved, the preparation process is environmentally friendly, pollutants are not generated or discharged, the prepared CuGa2 thin film is even in thickness, and under the dry friction condition, the CuGa2 thin film has good friction reduction and wear resistance effects.