Abstract: To improve the low routine test efficiency of a hydraulic operating mechanism which is the core component of a certain type 550 kV circuit breaker (CB), a simulated load device with convenient installation and equivalent characteristics of this specific type circuit breaker is designed. Firstly, the actual load characteristics of the circuit breaker are analyzed and found, including the maximum reaction force and its corresponding position in the whole CB travel. Secondly, the hydraulic buffer is designed according to the obtained force situation. Finally, the performance of the hydraulic buffer is tested on the hydraulic operating mechanism. The final test results show that the characteristics of the simulated load device are equivalent to the circuit breakers, and which has he advantages of high life, easy installation and maintenance free. After its application, the simulated load device has greatly improved the routine test efficiency of the hydraulic operating mechanism.