The research on forming of arched structure, especially with closed feature, is of great significance in the field of 3D printing of metal parts. In this paper, an overhanging arched structure was formed by slant forming method with hollow laser beam inside power feeding. The overhang deposition method was proposed to eliminate the defects of the closed part that were the raised top and the recessed downside. The influence of slant angle, loading time, loading power and other parameters on the vertical fluidity of molten pool was analyzed, and the theoretical model of the vertical displacement of molten pool was established. The arched closed structure was successfully obtained by means of the technology of slant laser cladding forming with coaxial inside-beam powder feeding and the overhanging deposition method of molten pool. The test results show that the defects of the closed part that were the raised top and the recessed downside has been eliminated successfully by layered filling with variable angles and parameters and the minimum wall thickness of the closed part was 3.2mm that have met the requirements of design size.