The invention discloses a surface polishing method and a surface polishing device of a thin-wall expanding pipe. According to the invention, automation control is adopted so as to greatly save labor power, improve efficiency and obtain high precision; a low-temperature alloy (with the melting point range of 50-80 DEG C) is adopted as a filling medium to fix and support the thin-wall expanding pipe, so that the defect that a common filling material cannot effectively be filled is overcome; and skin effect under intermediate frequency heating is combined to fast melt the low-temperature alloy to remove the filling material, so that the polished finishing product ratio is high and the polishing quality is good. With the adoption of profiling position of a positioning device of the polishing device during the process of polishing the expanding pipe, positioning data can be transmitted to a control system for curve data fitting in real time, the position that a polishing head should reach can be figured out according to the outer outline shape of the expanding pipe in real time, and the polishing can be performed by the drive of a servo system, so that the precision of the shape and the size of the expanding pipe can be effectively ensured; and the polishing device is high in degree of automation, so that the labor intensity is reduced, and the danger to human health from powder can be prevented at the same time.