The invention discloses a deep dehydrating system device for natural gas. The device is characterized by comprising a filter separator, a first super-gravity machine, a condenser, a poor/rich liquor heat exchanger, a pressurizing pump, a buffer tank, a reboiler, a second super-gravity machine, a flash tank, a conveying pump, a first stop valve, a second stop valve, a third stop valve, a fourth stop valve, a fifth stop valve, a reducing valve, a flowmeter, a vacuum pump, a gas-liquid separator and a three-way valve. The invention discloses a dehydrating method. According to the device, the purity of regenerated triethylene glycol poor liquor can be improved to 99.99wt%. By using the triethylene glycol poor liquor as an absorbent, the water dew-point at the natural gas outlet after water absorption in an absorption system is reduced to be below 35 DEG C below zero, preferably 45 DEG C below zero. The problem that the dehydrating depth of natural gas in the absorption system is low as triethylene glycol is not high in purity is solved, and the dehydrating treatment demand on low water dew point natural gas is met.