Abstract: 2, 3 Dimethyl benzoic acid was synthesized by the carboxylation of o xylene and CO2 with self made chloroaluminate ionic liquid as the catalyst. Process conditions, such as the type of chloroaluminate ionic liquid, reaction temperature, CO2 pressure, the quantity of catalyst, and activation, were studied.The results showed that the yield of 2, 3 dimethyl benzoic acid could reach 75% under the condition of 12 g ［BMIM］Cl·2AlCl3, 60 ℃, and 3 MPa. In conclusion, chloroaluminate ionic liquid could replace AlCl3 powder in carboxylation reaction. The Lewis acidity strength of different chloroaluminate ionic liquids, which were characterized using infrared spectroscopy probed by acetonitrile molecule, was correlated with the performance of carboxylation reaction. The result indicated that the Lewis acidity became stronger, and the catalytic activity enhanced upon increasing the molar fraction of aluminum chloride.