Abstract: The simple negative pressure-boosting circuit of air cycle air conditioning in room is presented. Thermodynamics parameters of every working state are caluclated. The problems of key technology to be solved are discussed. The conclusion is that the refrigeration efficiency of air cycle air conditioning in room can reach to 1.72, the heating efficiency also can reach to 1.71. This new kind of air cycle air conditioning in room is friendly environmental and promisimg.