The invention relates to a humidity controller. The controller comprises a housing and a support frame is configured in the housing. The support frame (2) is arranged at a central section of the housing and a spindle sleeve is fixed. A coupling spindle is arranged in the spindle sleeve; the upper end of the coupling spindle is fixedly connected with a central end of a coil spring; the coil spring is fixed on the support frame; and the lower end of the coupling spindle is fixed connected with a disc. A gap is opened at the perimeter of the disc; and a photoelectric switch is arranged at a position that is on the support frame and is at one side of the gap. Therefore, when the humidity indoors is changed, the length of the coil spring manufactured by moisture sensing sheet will be expanded or contracted with the temperature; the expansion or contraction of the coil spring will drive the coupling spindle to make clockwise or anticlockwise rotations, so that the disc is driven to be make rotations. When the gap arranged at the perimeter of the disc is rotated at the position where the photoelectric switch is located, the photoelectric switch make motions and thus a humidifier or a dehumidifier is driven to work, so that an objective of humidity control is achieved. According to the invention, the humidity controller has advantages of simple structure and low price.