Silicon (Si) modification layer on silicon carbide (SiC) surface is widely used in space optical systems. To achieve high-quality optical surface, the technology of ion beam figuring (IBF) is studied. The radio frequency ion beam source is introduced briefly. Then the removal function experiment is studied. The volume removal stability of the IBF reached 97% in 10 h continuous working testing. The parameters of the IBF removal function are calculated by Gaussian fitting including the removal rate and the full-width half-maximum. Then the removal function results are used in practical fabrication. The workpiece is a plane with Si modification layer on SiC surface. After 148 min processing IBF, the final surface error reaches 1.2 nm RMS.