Abstract: A method and a test device of air control drying were introduced. Conditional selection of double condenser and evaporater heat pump system was combined with rapid adjustment of rotation of compreser to adjust temperature and humidity of circulational air in drying system. Automatic control of different ratios including air composition was completed by using Expert-PID adjustnent method. Experiments indicated that this device is suitable for air control drying of different products and there was evident effect of oxygen content in drying process on the quality of dried product.