Abstract: This paper describes a compact liquid cooling unit designed for an airborne active phased array fire control radar. An approach to design of the unit is elaborated, including its structural layout,operating principle, device composition, design concept, in response to radar忆s application background and engineering demands. This design is then validated by performance test and environmental experiments, and proves to be fully applicable. Compared with similar airborne liquid cooling units the volume is reduced by 8. 6% and its weight is reduced by 26% under the same heat exchange condition. This study can be used for reference to design cooling unit and cooling system of the electronic devices such as airborne radars.