In the present study, a computer program was developed for simulating the steady-state performance(COP, capacity, power consumption and etc.) of the multi-airconditioning systems using R410A. The computer program consists of several subroutines for simulating indoor units, outdoor unit, compressors, and expansion devices(capillary tube and electronic expansion valve), and for estimating the thermodynamic and transport properties of the refrigerants and moist air. In order to validate the simulation program, a series of case studies were carried out. The results of the simulation showed a good agreement with calorimeter test results of the actual multi-airconditioning systems using R410A.