The invention belongs to a chemical field and particularly relates to a method for preparing 2-methylindoline, which synthesizes the 2-methylindoline by catalytic hydrogenation of 2-methylindole in acidic ionic liquid, wherein the acidic ionic liquid is ionic liquid of quaternary ammonium salts with a structure shown below; and in the structure, R1, R2 and R3 are alkyl or oxyalkyl, X is hydrogen sulfate, dihydrogen phosphate or benzene sulfonate, and n is equal to 2, 3 or 4. In the invention, the reaction conditions are easy to control, the raw material source is rich, the selectivity is high, the yield is high, the environmental protection effect is remarkable, the operation process is simple and convenient, and requirements of scale production can be met.