The present invention discloses a dehumidifier and a float assembly thereof, wherein the float assembly comprises a float, a press plate, a suction pipe, and a rotation shaft. The float, the suction pipe, and the press plate are fixedly connected to the rotation shaft respectively, and the suction pipe and the float are arranged at the same side of the rotation shaft, so that the suction pipe is driven by the float to synchronously rise up or fall down along with variation of water level of a water tank; the press plate is driven by the float to control a draining pump to drain when the water tank is at the high water level, thereby realizing automatic drainage. The present invention doesn't need to dispose both a fixed water tank and a movable water tank.