Compared with the traditional organic-coated fiber, the metal-coated fiber has significant advantages such as high thermal stability and anti-vibration interference. However, the continuous online preparation technology of metal-coated fiber is still in the research and development stage in China, which directly leads to the failure of large-scale continuous production of metal-coated fiber, and to a certain extent, limits the rapid development of high-power fiber lasers in China. An on-line fabrication device of metal-coated fiber based on molten metal condensation coating method was proposed and developed. Coupling with the fiber drawing tower, it can realize metal coating while drawing, and the coating thickness can be controlled. Aluminum coated fiber with uniform coating, good surface quality and stable diameter had been successfully fabricated. The influences of fiber inlet temperature, liquid aluminum temperature, mold aperture and contact distance on the coating quality of metal coating were discussed. By theoretical analysis and practical experiment, the optimum temperature of aluminum liquid is 663-690 ℃, and the linear decreasing relationship between the thickness of coating and the temperature of aluminum liquid was obtained. The relationship between drawing speed and cooling distance was calculated. The optimal aperture size of screw of ceramic upper and lower die and the contact depth between optical fiber and liquid aluminum were given. The research results provide a solution to the problem of mass production of metal-coated fiber and lay a foundation for breaking the international technology monopoly.