Abstract: The 1-butyl-3-methylimidazolium phosphotungstic acid ionic liquid(BMIM₃PW₁₂O₄₀), was prepared from N-methylimidazole, bromo-n-butane and phosphotungstic acid. It was loaded on amino-functionalized Fe₃O₄(Fe₃O₄-NH₂) by ultrasonic impregnation method. A jujube-like structureBMIM₃PW₁₂O₄₀/Fe₃O₄-NH₂ magnetic composite was obtained. TheBMIM₃PW₁₂O₄₀/Fe₃O₄-NH₂ magnetic composite was characterized by FTIR, XRD, XPS, TEM, vibrating sample magnetometer (VSM) and SEM. TheBMIM₃PW₁₂O₄₀/Fe₃O₄-NH₂ magnetic composite was used as catalyst for the oxidation of n-octane simulated oil samples with dibenzothiophene (DBT) as sulfur source, via hydrogen peroxide as oxidant. The effects of ultrasonic time, H₂O₂ usage amount, reactive temperature and catalyst dosage on desulfurization were investigated. The catalytic desulfurization mechanism was discussed. The results showed that the optimized catalytic degradation rate reached 88.13% with the H₂O₂ to DBT n(O):n(S) molar ratio of 8:1 at 323 K when 0.5 g/LBMIM₃PW₁₂O₄₀/Fe₃O₄-NH₂ was used for the desulfurization of simulated oil sample with the concentration of dibenzothiophene at 500 mg/g for 10 mins. After reused for 5 times, the catalytic degradation rate decreased only 2.51%, which indicated that theBMIM₃PW₁₂O₄₀/Fe₃O₄-NH₂ magnetic composite was of good catalytic desulfurization performance and can be reused. The primary desulfurization mechanism study shows that the catalytic active center might be the heteropoly acid anion of theBMIM₃PW₁₂O₄₀/Fe₃O₄-NH₂ magnetic composite, with the Fe₃O₄-NH₂ serving as a supporter and the ionic liquid as a cooperative compatibilizer, respectively.