The dynamic characteristics of hydraulic operating mechanisms are of great significance to the reliability of high-voltage circuit breakers (HVCBs). Due to the lack of cosimulation models that consider the coupling links of different physics, previous research works were limited to the analysis of some discrete parts. The purpose of this study is to propose a novel technique for the cosimulation of a hydraulic operating mechanism (OM). For that aim, the lumped parameter method is adopted to model the hydraulic system, and the finite-element analysis method is employed for the transmission mechanism. Then, a distributed parallel-type cosimulation framework is applied, and the coupling links between different subsystems are achieved by input‒output variable exchanges with shared memory. Experimental validations and simulation applications are implemented in a 550-kV HVCB. This proves that the proposed cosimulation model can accurately capture the dynamic responses of hydraulic OMs, including predicting the dynamic responses induced under different operation parameters and quantifying important features such as stress distributions and dynamic response evolution patterns.