Abstract: To solve the overheat problem of a sealed electronic enclosure of radar in long-time operating, the factors influencing its heat dissipation of inner modules are investigated. Temperature experiments are conducted, and then theoretical calculation and numerical simulation using Icepak software are completed. Based on experimental measurement and numerical simulation, the overheat problem is solved by decreasing the thermal conduction resistance and improving the heat transfer capability. Environment test results verify the validity of the proposed method which ensures the normal operation of the enclosure in high temperature and meets the design requirements.