To improve the heat dissipation performance of the high power solid state laser, a spray cooling system is designed based on the refrigeration cycle, with R600a as the coolant. The heat transfer performance of the closed spray cooling system is studied by experiment. The results show that the heat source surface temperature is affected by the nozzle inlet pressure and spray chamber evaporation pressure. And it is more effective to reduce the surface temperature by reducing the spray chamber evaporation pressure. For example, the decrease of 50 kPa evaporation pressure can result in the reduction of 8 ℃ of the surface temperature. The nozzle inlet pressure and spray chamber evaporation pressure also have a combined effect on the heat transfer coefficient. It is found that the heat transfer coefficient is up to 35000 W/(m2·℃) in the experiment. In addition, the surface temperature standard deviation is mainly affected by the nozzle inlet pressure, and it is hardly affected by the increasing of pray chamber evaporation pressure.