Abstract: The thermal design of HAHS(High-altitude and High-speed) UAV airborne electronic equipment is studied in this paper. To solve the problem caused by shortage of cooling medium, a cooling method is put forward which combines structure thermal inertia and fluid nitrogen cooling. Based on this method, two coolingunits are designed with different structures. After several experiments, the temperature distributions of theelectronic equipment at different cooling liquid supply are obtained, and how fluid nitrogen consumption affects unit temperature distribution is also analyzed. The experiment result shows that despite extreme lack of cooling medium, this cooling method can ensure that the airborne electronic equipment works within allowable temperature range. This design method can provide a useful reference for future similar thermal design.