It is very important to keep different pressure among rooms with different cleanness in pharmaceutical factories, semiconductor factories and so on. However, a trouble, that caused by the room pressure changes, is frequently detected at commissioning systems and results in significant losses of time and money. A method of design review, by use of a simulation, is proposed in this paper to prevent trouble of room pressure change. The commissioning test removes the causes of the trouble in the design stage. This paper notes simulation results of the air-conditioning systems. The simulator is made by MATLAB and SMULINK. The developed method of this simulator is expounded by use of Base-model in which all kind of elements of air-conditioning components are included. When room pressure of the Base-model is controlled, the simulator measures room pressure change and flow rate change. The simulator can evaluate the systems beforehand only by design information. As an example of evaluation of the systems, an actual air-conditioning system, where the room pressure change trouble occurs, is verified. It adequately explains the cause and solution of this trouble.