The invention discloses a method for removing DBDS in mineral insulating oil by an alkaline chitosan membrane. Through preparation of the alkaline chitosan membrane, DBDS is removed with the alkalinechitosan membrane, the obtained alkaline chitosan membrane and to-be-treated mineral oil are mixed and heated to 80-110 DEG C, reaction is performed for 0.5-1.5 h, filtration is performed, and the used alkaline chitosan membrane and the mineral oil after DBDS removal are obtained. The used alkaline chitosan membrane is regenerated, that is to say, the alkaline chitosan membrane obtained after themineral oil is removed is washed with an organic solvent and is reused. The alkaline chitosan membrane has the advantages of simple preparation process, quick and convenient removal of DBDS, and convenient separation of oil products and the membrane, and the used membrane can be recycled and reused after simple regeneration and alkalinization treatment.