The utility model discloses a closed composite cooling system. The system comprises a cooled device, an air cooler and a cooling water pump which are connected and form a circulation loop through a pipeline. The system also comprises a first plate-type heat exchanger, a second plate-type heat exchanger, a water chilling unit, a cool storage tank, a buffer tank, a first cold pump and a second cold pump. A heat side of the first plate-type heat exchanger and a heat side of the second plate-type heat exchanger are connected in series in the circulation loop. The first cold pump, the water chilling unit, the cool storage tank and the buffer tank form a cool storage loop. The first cold pump, the water chilling unit, a cold side of the first plate-type heat exchanger and the buffer tank form a first cold release loop. The second cold pump, the cool storage tank and a cold side of the second plate-type heat exchanger form a second cold release loop. By using the closed composite cooling system of the utility model, a design temperature can be obviously lower than a limiting temperature of a local place; the structure is compact; an amount of air heat exchangers is reduced; a design capacity of an air cooler is fully used; cost is reduced so that an application region of a closed-type circulating pure water cooling system is expanded.