The invention relates to the field of treatment of plant fibers and particularly relates to a method for separating cellulose and lignin from a plant fiber raw material by utilizing ion liquid. According to the invention, the method comprises the following steps of: 1) mixing DMSO (Dimethylsulfoxide) and the ion liquid according to a mass ratio of 1: 4-9 to be used as a solvent, and adding the plant fiber raw material; 2) dissolving at 80 to 140 DEG C for 4-48 hours to obtain a reaction mixed liquid; 3) filtering and separating the reaction mixed liquid by a stainless steel filter screen or a nylon filter cloth, adding water into the obtained filtrate, and depositing a mixed extract of the cellulose and the lignin; 4) washing and extracting a mixed extract of the cellulose and the lignin by a water/DMSO mixed solvent, and filtering to obtain mixed liquid of a cellulose solid and lignin/DMSO/water; 5) drying the cellulose solid to obtain a cellulose product; and 6) decompressing and distilling the mixed liquid of the cellulose/DMSO/water to obtain a cellulose product. The method, provided by the invention, is simple, feasible and high in purity of the obtained cellulose.