Based on the analysis of the outdoor weather condition in Chinas hot summer region, it is found that the full fresh air mode can work in the whole winter and half of the time in transition season. Thus, about 30%-60% runtime of the artificial cold source can be reduced. It studies the control strategies at different conditions of indoor load, ventilation and indoor air temperature and humidity by analyzing two control modes-enthalpy control and temperature control. It shows that the higher the indoor load is, the more efficient the full fresh air mode is. And the airflow is better to be set as 6~8 h-1. Since the indoor air parameter has great influence on energy saving, it is necessary to set different indoor air parameters in different seasons by taking the effect of temperature difference on human thermal comfort into consideration. It is also found that the enthalpy control mode can be used in winter and in transition season, while the temperature control mode can be applied in summer. If the full fresh air mode were adopted, it would cut down the energy consumption by 100~180 kWh/m2 and the carbon emission by 30~50 kg/m2 each year.