Abstract: Final optics play an important role in Inertial Confinement Fusion (ICF) system. In this paper, the online inspection technology for final optics damage was studied in order to build a final optics damage online inspection system for ShenGuang-Ⅲ(SG-Ⅲ) prototype device. According to the assignment of final optics in optical module, a zoom telescope optical system with high resolution was designed by CODEV to meet the testing requirement. Based on the assignment of optical modules in target chamber, the positioning mechanism was designed to focus and switch the beamlines and the optics accurately and rapidly. At last, an off-line simulation experiment based on SG-Ⅲ was carried out. The result shows that the MTF at the spatial frequency of 68 lp/mm is greater than 0.4, 80% of the energy is distributed within 22 CCD cells. Between 1.8 m to 2.8 m, the resolution of the optical detecting mechanism can reach 160 m. The defects can be tracked when their diameter is up to 60 m by image processing method. The precision of the positioning mechanism is better than 13 arc sec.