Considering the negative effects of the presence of mercaptan and methanol in light oils on their use in fuels and petrochemical feedstock, ionic liquid extraction was developed in this study as an efficient, economical and environmentally friendly method for the removal of mercaptan and methanol. Based on COSMO-RS calculation results and screening experiments, the ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim] [Ac]) is a good choice for the simultaneous removal of mercaptan and methanol. In this work, the effects of the IL/model oil mass ratio, equilibrium time, temperature and cycle times on the mercaptan/methanol removal performance of [Bmim] [Ac] were systematically studied. The experimental results are in line with the simulation results. For [Bmim] [Ac], after only one single extraction process of 11 h, 95.8% BM (BM-content drops from 200 ppmw to 8.34 ppmw) was removed at 25 degrees C and 1:20 (w/w) of IL: model oil. Meanwhile, after only one single extraction process of 4 h, 99.5% MeOH (MeOH-content from 5000 ppmw to 25.48 ppmw) was also removed at 25 degrees C and 2:5 (w/w) of IL: model oil. In addition, the experimental result of industrial post-MTBE C-4 is consistent with that from model oil. In this work, the extraction mechanism of [Bmim] [Ac], particularly the role of the COO- group, was also experimentally and theoretically studied. The results of simulation and NMR experiments show that the anion [Ac](-) provides the hydrogen bonding interaction, which indicates the mechanism by which [Bmim] [Ac] extracts BM/MeOH.