Abstract: A compression cooling system of a shoe midsole comprises mainly a main body, an air sac and an air duct. The air sac is disposed in the main body such that the air sac is corresponding in location to the heel of a shoe. Two one-way valves are disposed on predetermined portions of the air sac. The air duct has one end that is connected with one of the two one-way valves and has another end that extends to reach the upper surface of the shoe midsole. The treading and the jogging actions of the foot wearing the shoe bring about the pumping effect of the air sac, thereby generating a stream of suction to cause the air inside and outside the shoe to circulate.