n-Butyl acetate (NBA), a key organic chemical intermediate, is widely applied in coatings, paints, inks, printing, electronics, and leather processing. The primary method for NBA production is the esterification of n-butanol. During this process, a mixture of n-butanol and NBA is produced, and it is necessary to separate them. However, the azeotrope formed between NBA and n-butanol at atmospheric pressure makes conventional distillation ineffective. In this work, three ionic liquids (ILs), 1-ethyl-3-methylimidazolium acetate ([EMIM][AC]), 1-ethyl-3-methylimidazolium dimethyl phosphate ([EMIM][DMP]), and 1-ethyl-3-methylimidazolium diethyl phosphate ([EMIM][DEP]) were screened as extractants using the COSMOthermX software based on COSMO-RS theory, with selectivity as the main indicator, combined with the viscosity of ILs. Liquid-liquid equilibrium (LLE) data for the ternary systems (n-butanol+NBA+ILs) were measured at 303.15 K and atmospheric pressure. The reliability of the LLE data was verified via Othmer-Tobias, Bachman, and Hand equations. The extraction performance of the three ILs was evaluated by selectivity and distribution coefficient, and the non-random two-fluid (NRTL) model was used to correlate the LLE data. Finally, the separation mechanism of the three ILs was explored by means of σ-profile and σ-potential analysis. The results indicated that the linear correlation coefficients (R2) of the Othmer-Tobias, Bachman, and Hand equations for the ternary LLE data all exceed 0.95, demonstrating high reliability of the data obtained in this work. The distribution coefficients (D) and selectivity (S) of the three ILs were all greater than 1, confirming their suitability for separating the n-butanol and NBA mixture. The separation performance followed the order of [EMIM][AC]>[EMIM][DMP]>[EMIM][DEP]. All three ILs were deemed suitable for separating the n-butanol and NBA mixture. The root mean square deviation (RMSD) between the results calculated by the NRTL model and the experimental data was less than 3%, indicating that the NRTL model was highly applicable for describing the LLE behavior of the n-butanol-NBA-IL ternary system studied in this work. There was a stronger hydrogen bond interaction between ILs and n-butanol, so ILs could separate n-butanol from its mixtures with NBA. The order of the interaction strength between the three ILs and n-butanol was [EMIM][AC]>[EMIM][DMP]>[EMIM][DEP].