The invention relates to a natural gas dehydration system and a dry gas water dew point test method thereof. The system comprises a wet gas inlet, a primary filtering device, a triethylene glycol contact tower, a lean glycol/dry gas heat exchanger, a triethylene glycol regeneration device, a triethylene glycol sampling device and a temperature detection device, wherein the gas inlet of the triethylene glycol contact tower is connected to the primary filtering device, the gas outlet of the triethylene glycol contact tower is connected to the first input end of the lean glycol/dry gas heat exchanger, the first output end of the lean glycol/dry gas heat exchanger outputs dry gas, the liquid outlet C2 of the triethylene glycol contact tower is sequentially connected to the triethylene glycol regeneration device and the second input end of the lean glycol/dry gas heat exchanger, the second output end of the glycol/dry gas heat exchanger is connected to the liquid inlet C3 of the triethyleneglycol contact tower, the temperature detection device is connected to the gas inlet of the triethylene glycol contact tower, and the triethylene glycol sampling device is close to the second input end of the lean glycol/dry gas heat exchanger, and is connected to the triethylene glycol regeneration device. According to the present invention, the system has characteristics of low cost and wide application range.