The dynamic characteristics of hydraulic operating mechanism is of great significance to the reliability of high-voltage circuit breaker (HVCB). Due to the lack of co-simulation models considering 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 co-simulation of hydraulic operating mechanism (OM). For that aim, lumped parameter method is adopted for the modeling of hydraulic system and finite element analysis method is employed for that of transmission mechanism. Then, distributed parallel type co-simulation framework is applied, and the coupling links between different subsystems are achieved by input-output variables exchange with shared memory. Simulation and experimental validations are implemented in a 550KV HVCB. It proves that co-simulation model can accurately capture the dynamic responses of hydraulic OM, including predicting the dynamic responses under different operation parameters and quantifying important features like stress distribution and dynamic responses evolution.