In the building fire situations, smoke is one of the principal causes of human deaths or injuries. Preventing migration of smoke to escape routes is extremely important. Most of the existing buildings especially the high - rise buildings, are equipped with fire alarm systems and springkler systems but not smoke control systems. Smoke control systems cannot be designed and analized manually. A C-language program has been developed to analyze the systems. In this computer program, a building is represented by a network of spaces or nodes, the stairwells and other shafts are modeled by a vertical series of spaces. Simulation of smoke control system begins either by supplying amount of outside air into any level of shafts or other building spaces or by exhausting smoke in the fire zones. Fire is then supposed to take place at any floor and in different situations. For each situation, the pressures throughout the buiding and flow rates through all the flow paths are obtained by iteratively solving the airflow network according to the mass balance equations. The appropriate pressure and flow rate that can cover all envisaged situations are used to determine the air handling fan.