Dehumidifiers are widely used in offices, libraries, computer rooms, precision instrument rooms, hospitals, storehouses, etc., keeping archives, materials, electrons, optical instrument, precision equipment and other valuables from mould, mildew, and odours. Especially in rainy seasons, dehumidifier is a protector of garment, leatherware and electric appliance, and becomes a health worker of lying-in women, babies and elders who suffers from rheumatism or respiratory diseases.