The system air-conditioner, which has one outdoor unit connecting several indoor unit units, can provide more energy saving and better environmental conditions than the conventional air-conditioning systems. But it is difficult to experimentally analyze behaviors of system air-conditioners due to various load conditions and combinations of indoor units. Therefore, it is important to develop a cycle simulation program for predicting the performance of system air-conditioners without complex experiments. The cycle simulation program for system air-conditioners consists of several subroutines for simulating indoor unit, outdoor unit, compressor, and expansion devices, and for estimating the thermodynamic and transport properties of the refrigerants and moist air. It was programmed with Digital Visual Fortran for the main simulation code and Visual Basic for the graphic user interface.