Four imidazole ionic liquids with different anions were synthesized by a two-step method, and their structure and acidity were characterized by FT-IR, 1H NMR, 13C NMR, TG, Hammett acidity function. Using α-pinene esterification-saponification reaction as a probe reaction, the selectivity of four ionic liquids to n-borneol was investigated. The result shows that the anion is [HSO4]-the best selectivity for borneol, which is consistent with the result calculated by Hammett's acidity function. [Bmim-SO3H]HSO4 for further process research, and the optimized process conditions are: ionic liquid is 8% of the mass of turpentine, n(turpentine):n(acetic acid)=1:3, reaction temperature is 120℃, reaction time is 8h, and the amount of cyclohexane is 35ml. Under these conditions, the conversion rate of α-pinene was 100%, and the selectivity of n-borneol was 39.83%, accounting for 92.58% of the total borneol. Among them, the role of ionic liquid is to provide H to protonate α-pinene to form carbanion, HSO4- stabilizes non-classical carbanion, and forms a complex with acetate, making the reaction to generate borneol more easily. [Bmim-SO3H]HSO4 has high activity after repeated use for three times, the conversion rate of α-pinene is still 99.76%, and the selectivity of borneol is 35.45%.