In order to make the buffer play the best damping effect at the end of opening of circuit breaker and spring operating mechanism, so as to ensure the curve of opening end of the circuit breaker be smooth and without a rebound, and to ensure the breaking performance of the circuit breaker, it is necessary to perform jointly modeling and simulating calculations for the buffer and circuit breakers. Based on the throttle principle and multi-body system dynamics calculating method, this paper establishes the calculating model for hydraulic buffer in spring operating mechanism, compiles and calculates dynamic link library of damping force by C language and interacts with ADMAS simulation, finishes the simulation of hydraulic buffer in spring operating mechanism. The simulation results are compared with the actual test results, and the correctness of the calculation and simulation methods is verified. A technical route combining simulation calculation and experiment is practiced, which establishes a foundation for actual engineering application, the design of hydraulic damping device and research on breaking technology of circuit breaker.