A dehumidifier is composed of a compressor, two devices (evaporator and condenser), a fan, a water tank (direct discharge pipe), a casing, and a controller. Its working principle is that the fan sucks humid air into the machine, and the compressor refrigeration system lowers the surface of the evaporator to below the dew point temperature of the air. At this time, when the humid air passes through the evaporator, the water in the air will decompose and attach to the surface of the evaporator (note: just like in summer when we take out a bottle of water from the refrigerator, there will be a layer of condensed water on the outside of the bottle). The water will flow along the hydrophilic platinum on the evaporator to the collection tank and then flow to the water tank or drainage pipe for discharge. The dehumidified dry air will be heated by the heat recovered by the condenser and discharged outside the machine. Circulation achieves a drying effect in humid air rooms.