Abstract: The biodiesel produced from the waster cooking oil,such as gutter oil,usually contains a certain amount of sulfide,which would cause the environment pollutions during the combustion. In order to solve the above problems,this study investigated the migration of sulfides during the traditional acid-base two-step process to prepare biodiesel. Then,using ionic liquid（HnmpH₂PO₄）as extractant and catalyst,H₂O₂ as oxidant,the extraction oxidative desulfurization of gutter oil biodiesel was studied,and the desulfurization reaction process was optimized by orthogonal experiment. The results show that the reagents,materials and operating conditions used in the preparation of biodiesel did not increase the sulfur content and change the form of sulfide in biodiesel products.The existing forms and contents of sulfides are related to the sulfides in the raw oil itself. The sulfides in biodiesel mainly exist in the form of alkylbenzothiophenes and alkyl dibenzothiophenes. Under the conditions of reaction temperature 75 ℃,volume ratio of biodiesel to ionic liquid 10∶3,volume ratio of biodiesel to H₂O₂ 10∶1.2,and oxidation time of 70 min,the desulfurization rate of biodiesel can reach 94%,which meets the requirement of sulfur content ≤ 10 mg/kg in the latest national VI diesel emission standard（GB 17930—2016）.