Abstract: Shipboard electronic equipment operates in a severe environment of high temperature and high humidity for a long time. In order to meet the increasing requirements of function and performance, the chassis mainly adopts the sealed form. Compared with the ventilation chassis, the sealed chassis is more difficult to dissipate heat, especially for the electronic equipment with small size and large heat consumption. In this paper, a shipboard high-power sealed chassis is studied. The scheme of heat dissipation is determined by the thermal analysis and theoretical calculation. The correctness of the theoretical calculation is verified by Flotherm software modeling, grid division, simulation analysis and so on. Finally, the simulation results are checked by experiments. This study provides a reference for the thermal design of small-size and high-power sealed chassis.