Abstract: Heat dissipation of power semiconductor devices is an important factor threatening the safe operation of solid state circuit breakers, and maintaining the junction temperature of operating equipment under operating conditions remains a major challenge. This paper studies the basic theory of thermal design involved in low-voltage solid-state circuit breaker, establishes the thermal simulation model of the main circuit of low-voltage solid-state circuit breaker including PCB, MOSFET three-dimensional structure and radiator, analyzes the heat transfer path of the heat source of the main circuit of low-voltage solid-state circuit breaker, and designs the heat dissipation scheme of the solid-state circuit breaker. FloTHERM is selected for the design and research of low voltage solid state circuit breaker cooling system. Finally, the heat dissipation experiment of low-voltage solid-state circuit breaker is carried out. The proposed heat dissipation scheme can increase the rated working current of low-voltage solid-state circuit breaker by 32.1% without changing the volume of low-voltage solid-state circuit breaker and the number of MOSFETs.