The interaction mechanism of the typical ionic liquid (IL) 1-methyl-3-butyl imidazolium hexafluorophosphate (［BMIM］［PF6］), imidazolium ionic liquid with hydroxyl group and nonylphenol (NP) was studied through infrared (IR) spectroscopy and quantum chemical calculations for density functional theory. The results indicated the hydrogen bonds could not be found in the IR spectra before and after IL ［BMIM］［PF6］ extracting NP while the absorption peaks of the hydroxyl group of the ILs containing hydroxyl group have red shifts after the ILs extracting NP. It could be seen in the theoretical calculation that the cation ［BMIM］+ of ［BMIM］［PF6］ has the C—H…O hydrogen bond interaction with NP. The O—H…O type hydrogen bond could also be formed between the cation ［C4H9OHIM］+ of the IL with hydroxyl group and NP. It could be concluded through the two mechanism study methods that the strength of hydrogen bond between the IL with hydroxyl group and NP was bigger than the one between the typical IL ［BMIM］［PF6］ and NP, followed by the bigger extraction efficiency of NP by the former, which coincided with the extraction experiment result.