Abstract: Excessive temperature rise will accelerate the aging of vacuum circuit breakers and reduce mechanical strength. The heat dissipation optimization design of circuit breakers is of great significance to the stable operation of circuit breakers. Therefore, the electromagnetic simulation model of circuit breaker using for large capacity pumped storage was established. The electromagnetic loss of 12.5 kA was calculated. The total loss based on the contact resistance was obtained. A natural convection simulation model of circuit breaker including considering convection, conduction, and radiation was established. Then the heat dissipation structure of circuit breaker was designed and optimized to enhance natural convection and radiation. The results show that the maximum temperature rise of the circuit breaker is 133.7 K under the conduction current of 12.5 kA, and the radiation power accounts for 23%. By adding heat sinks and heat pipes, the maximum temperature rise can be reduced to 109.5 K. Increasing the surface emissivity of the circuit breaker component can achieve a low-cost radiation power increase and further reduce the maximum temperature rise to 96.9 K. Finally, the reliability of the simulation results is verified by carrying out the steady-state current temperature rise experiment of the circuit breaker. The average error between the simulation and experiment of the temperature rise of the monitoring point is less than 2.1 K.