Abstract: We developed a method in which Dionex "Pre" online sample preparation technique was used to remove chloride by Ag cartridge and Na cartridge. This method is applicable to a wide range of samples and is simpler than off-line approach. Each Ag cartridge carries on 400 consecutive injections (25 microlitre each) of 1% NaCl solution, and the removal efficiency is still above 99%. The separation of anions was carried out by high capacity hydroxide selectivity IonPac AS11-HC gradient separation column while Eluent Generator was employed to generate gradient KOH eluent online automatically. Two valves were switched to finish the injection. The system removes chloride well online for different matrix as analysis grade salt and sodium chloride. The detection limits of bromate, chlorate, chlorite, nitrite, nitrate and sulfate are less than 10 μg/L, and the recoveries are between 80% and 110%. This method holds the advantages of easy-operation, good reproducibility, lower operation cost etc and is more convenient than off-line approach.