The knowledge system of mechanical symmetry was briefly summarized, and the application in the field of mechanical design and process planning was analyzed. The mechanism of structural symmetryfunctional symmetryprinciple symmetry included in mechanical symmetry was studied, the basic idea of rapid fixture design based on mechanical symmetry knowledge was pointed out. The information model of fixture based on symmetry knowledge was established, and the key technology and architecture of rapid fixture design under the mechanical symmetry knowledge were put forward. According to the symmetry principle, on the basis of the secondary development of SolidWorks, a CAFD system applied to the manufacture of automobile synchronizer was developed, and the rapid fixture design based on the mechanical symmetry knowledge was realized. The practicability and availability of the system were verified.