The invention discloses a direct contact type hygrostat based on compressor frequency control and a method thereof. The hygrostat comprises a cabinet, a fan, a compressor, a condenser, a water tank, a throttle valve, an electromagnetic reversing valve, a frequency converter and an evaporator. The compressor, the condenser, the electromagnetic reversing valve, the throttle valve and the evaporator are connected sequentially; the evaporator is arranged in the water tank, the air inlet of the fan is communicated with outside through a fresh air pipe, the air outlet of the fan is connected to a spraying pipe, and the spraying pipe is inserted into the bottom of the water tank from the right of the water tank; the top of the water tank is provided with a guide plate, and the air outlet of the top is provided with an air blowing pipe. According to the hygrostat, the water temperature is adjusted through the refrigerating capacity of the compressor, and the air dehumidification is changed by controlling the water temperature; the system further adopts the electromagnetic reversing valve, when air humidification is required, the system operates in a manner of a heat pump, the water temperature rises, and humidification is performed conveniently; the hygrostat is compact in structure and is specially adaptive to constant humid environment of a large showcase or antique storeroom.