The invention relates to a method for removing dissolved oxygen contained in alkali liquor. The method comprises the following steps of: introducing recycled alkali liquor inside a liquefied gas mercaptan removing system into a liquid inlet of a rotating packed bed, and introducing nitrogen with oxygen content not more than 0.1% v into the gas inlet of the rotating packed bed, wherein a gas phase and a liquid phase are subjected to contact mass transfer in the rotating packed bed; directly discharging oxygen-enriched nitrogen; extracting liquefied gas mercaptan from deoxidizing alkali liquor in an extraction tower, wherein the oxygen concentration of the deoxidized alkali liquor is 200 ppb. The method disclosed by the invention can realize the deep deoxidization of the recycled alkali liquor, prevents the reaction of generating a disulphide by generating sodium mercaptide oxidization in the liquefied gas mercaptan removing extraction tower, and can be used for enhancing the desulfurization effect of the extraction tower.