Abstract: Reducing sulfur content in FCC gasoline by using the complex of Brnsted acidic ionic liquid [BMIM]HSO4 and sulfuric acid as alkylation catalyst is introduced.The main factors for desulfurization rate of FCC gasoline such as reaction temperature，reaction time，acidity of complex catalyst，catalyst content and the amount of isoprene are studied.The results show that the desulfurization rate can be increased as the acidity of complex catalyst increases，and it may be increased obviously by adding a small amount of isoprene.Under the catalysis of 5% complex catalyst，the sulfur content of Shijiazhuang FCC gasoline can be reduced from 608mg/L to less than 105mg/L，and the content of Dagang FCC gasoline can be reduced from 122mg/L to 32mg/L by adding some isoprene at 30℃ when the reaction time is 120min，and the octan number of FCC gasoline is little changed.

Key words: ionic liquid, FCC gasoline, desulfurization, diolefin, alkylation