Abstract: Considering to controlling, the suitable live environmental condition for poultry can be defined as a twodimensional region, which is composed of dry ball temperature and relative humidity. In controlled condition, start from the live requirement of poultry and taking the maximum productivity as optimization target, the tolerant outdoor climate condition can then be calculated. Thus, an controlling region reflecting the live environmental condition and high productive capacity can be formed on the temperaturehumidity chart. This method can be used to evaluate the performance of poultry house ventilation system effectively.