Abstract: In order to keep the vitality of seeds over a long period of time, it is necessary to establish preservative environment under low temperature and low relative humidity. (0～-10℃, 35% relative humidity)This paper synthetically analyses the principle, merits and demerits of a variety of dehumidifiers. In accordance with the present situations of China, a dehumidifying system with two stages was put forward. At the first, the moisture in the air was removed by refrigeration and the temperature would drop down lower and lower in the seed storage. Secondly, a new type device named rotary dehumidifier reduced the moisture continuously under low temperature. So that the parameters in the storage such as temperature, relative humidity would be met.In this paper, the author not only described the structures and principles about the designed dehumidifier, but also described the test system and the effect achived in production. It was proved that this dehumidifying system was available for seed storage, It was runs steady and with remakarble achivement.