Ionic liquids (ILs) as a new kind of solvent have many unique attributes,e.g.negligible vapor pressure,good thermal stability and environment-friendly [1],which make them attractive and potential being used as a benign medium or solvent in chemical reaction and separation processes [2].The feasibility of using ionic liquids (ILs) as entrainers for the separation of the azeotropic mixtures of water and acetonitrile has been researched,and provided basic data for the industry calculation in this work.