The deep dehydration device uses high-efficiency molecular sieve adsorption method to dehydrate and purify raw natural gas, thus can effectively remove moisture and harmful composition such as H2S, SO2 and CO2 from natural gas and ensure high purify of natural gas. According to the volume and quality conditions of gas to be treated, different operation modes such as single-tower, double-tower, series or parallel towers can be used to actualize efficient and continuous dehydration and purification. The adsorption tower is equipped with high-efficiency filters for the front and back, which not only can prevent free oil and water from entering absorption tower and polluting molecular sieve, but also can prevent powder in dry natural gas from entering gas addition system and causing pipe obstruction. The molecular sieve can conduct repeated absorption and regeneration, with long service life and long change cycle.