Abstract: With the development of IR technology, more and more IR instruments were used on large telescopes. A cryogenic circumstance was necessary for IR instruments operation, this sets many technical challenges for opto-mechanical design. Optical parts need accurate mounting and positioning, meanwhile they must not be cracked or breaked by thermal stresses during cryogenic. In order to solve this problem, the kinematic mount theory was presented, detailed mechanical design for all reflecting mirrors, lens, filter wheels used in optical systems were proceeded and kinematic mount was realized by these designs. The conflict between firmly fixing the optics and preventing stresses within the optics during cooling was well settled via these kinematic mount designs. Optical system security and imaging quality during cooling were well ensured by these kinematic mount designs. The research results have important referential valve for mechanical and thermal design for IR optics system.