The utility model discloses a dehumidifier, which comprises a casing, a semiconductor dehumidifier, a heater, a controller, a temperature and humidity sensor and an LCD (liquid crystal display), wherein the semiconductor dehumidifier is composed of a semiconductor assembly, a cold piece, hot pieces and a cooling fan assembly, the semiconductor dehumidifier and the heater, which are fixed together, are installed in the casing, the controller is installed on a secondary chamber cabinet plate of a target device, the temperature and humidity sensor is installed in a cavity in which the temperature and the humidity are required to be controlled and away from a heating and dehumidifying integrated device, the controller is electrically connected with the temperature and humidity sensor, the semiconductor dehumidifier and the heater through data lines, the temperature and humidity sensor acquires temperature and humidity data in the casing and transmits the temperature and humidity data to the controller through the data line, and the controller controls operations of the semiconductor dehumidifier and the heater. The dehumidifier disclosed by the utility model carries out refrigeration and dehumidification by using the semiconductor dehumidifier, the absolute humidity of the environment is reduced, the humidity inside a cabinet is obviously reduced after the dehumidifier operates for a period of time, and the humidity does not reset immediately when the dehumidifier stops operating, thereby avoiding a disadvantage that dehumidifying equipment is required to be put into use again immediately when stops operating, and having the advantages of accurate dehumidification and good dehumidification effects.