High voltage circuit breaker is an important interrupting device in a power system network. The operating mechanism is a key component of circuit breakers. The action of hydraulic operating mechanism in circuit breaker is different from general hydraulic mechanism for its high speed, short operating time and high pressure. In this paper, the working principle of hydraulic operating mechanism of 252kv high voltage circuit breaker is introduced. The high response speed solenoid pilot direction control valve is analyzed. The dynamic characteristic of the valve affects the performance of the hydraulic operating mechanism. Mathematical models of the valve and system have been developed. Simulations are carried out with AMESIM, hydraulic simulation software, and ANSOFT, electromagnetic simulation software. The characteristics of the operating mechanism control valve are discussed with the consideration of the influence of the geometry and environmental parameters. As the result of the research work, the simulation models and results provide the effectively theoretical guidance for the design and optimization of hydraulic operating mechanism.© 2008 ASME