Provided are a rack mount server system, which has no damage to computation equipment even if a disorder occurs in a cooling device, which is easy to maintain, minimize power consumption, which has a simple structure, and which performs an efficient cooling, and a control method thereof. The system comprises: a rack housing; and a cooling zone which is placed in the rack housing, which stores a server, and which is forcibly cooled. The rack housing comprises a heat exchanger and an evaporator, which cool the cooling zone. The cooling methods of the cooling structure may be different in accordance with the internal temperature of the cooling zone and the external temperature of the cooling zone.