The Ritchey-Chretien (R-C) optical system, as a two-mirror reflective optical system, is the typical structural form of hyperboloid optical system and has important applications in modern optical engineering. To shorten the adjustment cycle and guide the mass production of high-precision system, taking the R-C optical system applied in a certain airborne star sensor as an example, a secondary-mirror adjustment mechanism was designed for the secondary-mirror with small diameter under the premise of taking the primary mirror as the adjustment reference, which realized the adjustment of six degrees of freedom of secondary-mirror, and explained the method involved in the adjustment and curing process. The stability of the design mechanism was verified by testing the system image quality before and after adjustment and environmental test. The test results show that the secondary-mirror adjustment mechanism can meet the requirements of system image quality, the whole-machine wavefront aberration PV value is better than (1/2)λ, the RMS is better than (1/15)λ, and the adjustment method attains the goal of guiding the mass production of high-precision system.