Nanjing Institute of Astronomical Optics & Technology (NIAOT) is investigating two types of sub-aperture polish technique for manufacturing aspheric components in large astronomical telescopes. One technique is computer controlled optical surfacing (CCOS). It removes material by a small polish tool through traditional mechanical and

chemical process. The other is ion beam figuring (IBF) technique. It employs a neutralized ion beam to physically sputter material form optical surface. Although the basic mechanism of the two techniques is different, they true share the same mathematical model and fabrication diagram which will be put forward firstly in this paper. Then tool design and material removal function in CCOS will be studied following by a fabrication instance using CCOS. After that some recent progresses achieved in IBF is presented. The last part will focus on the complementary relationship of CCOS and

IBF. Using them alternatively optimal combination of surface precision, efficiency and edge control could be obtained. Simulation is provided to support this view and experiment will be done in near future.