Abstract: Internal standard method for the determination of trace impurity by internal standard substance addition to eliminate the effects of operating conditions fluctuation on the results, improves the accuracy of the analytic result. By comparing the internal standard method and area normalization method for the determination of trace impurities in paraxylene, internal standard method has the advantages of high sensitivity, small interfering effect, and low detection limit. The optimized internal standard method is more suitable for the determination of trace impurities.