Tris(pentafluoroethyl)trifluorophosphate ([FEP])-based ionic liquids have been widely applied in many fields. For better understanding the properties of [FEP]-based ionic liquids, the interactions between 1-hexyl-3-methylimidazolium ([hmim])[FEP] and small molecules were investigated by molecular dynamics simulations in this work. The small molecules are water, methanol and dimethyl ether. The united-atom (UA) force fields were proposed for methanol and dimethyl ether based on AMBER force field. The densities, enthalpies of vaporization, excess molar properties, and diffusion coefficients of the mixtures were calculated, as well as the microscopic structures characterized by radial distribution functions. Both of the results of the excess energies and microscopic properties show that the strongest interaction is between [hmim][FEP] and dimethyl ether, whereas the interaction between [hmim][FEP] and water is the weakest. Moreover, [hmim][FEP] is more hydrophobic than [hmim] hexafluorophosphate ([PF6]), and the three solutes are mainly distributed around [FEP] anion. Tris (pentafluoroethyl) trifluorophosphate ([FEP]) - based ionic liquids have been widely applied in many fields. For better understanding the properties of [FEP] -based ionic liquids, the interactions between 1-hexyl- The small molecules are water, methanol and dimethyl ether. The united-atom (UA) force fields were proposed for methanol and dimethyl ether based on AMBER force field. Both the results of the excess energies and microscopic properties show that the strongest interaction is between [hmim] [FEP] and dimethyl ether, whereas the interaction between [hmim] [FEP] and water is the weakest. Moreover, [hmim] [FEP] is more hydrophobic than [hmim] hexafluoroph osphate ([PF6]), and the three solutes are mainly distributed around [FEP] anion.