Desulfurization unit of CNG gas station is the main device of the natural gas purification system. The Hydrogen sulfide is touched and dissolved with the water and generate foggy hydrogen sulfide aqueous solution with strong acidity, which would corrode mechanical equipment and do great harm to the strength and life of pressure vessel, the cylinder and pipe of the compressor and other stuff. If the desulfurization could not be announced in advance, the pipeline corrosion and the 'hydrogen embrittlement' of steel gas bottle would be caused easily. And do great harm to use equipment and personnel.