Abstract: The mechanical model of the framework, in synchronization (on/off) switching of a vacuum circuit breaker (VCB), was numerically simulated with software ADAMS/ANSYS, and experimentally evaluated with the lab-built test platform for the framework design optimization.The influence of the motions/mechanical properties of the components involved, including but not limited to the switching-on (off), static/dynamic forces, collision, friction, loads/constraints, stiffness of switch-on/off springs, welded junctions and stress/deformation distributions, on the reliability and service lifetime of ZN□-12 VCB framework was investigated.The simulated results show that the switch-on and stiffness/deformation of switch-on spring have a major impact.Moreover, the prototyped VCB framework, optimized and fabricated based on the simulated results, was tested for over 10, 000 switch-on/off cycles.The test result show that the design optimization of the framework significantly improved the reliability and VCB service lifetime.