A simple and rapid sweeping method for the online improvement of detection limit of some aromatic amines has been developed in this work. The optimum sweeping and separation conditions for 4-methylaniline, 3,4-dichloroaniline, 4-chloroaniline, and 4-aminophenyl were investigated in detail. Under the optimum conditions, the detection limits of these four aromatic amines ranged from 5.4 x 10(-10) to 4.6 x 10(-8)mol/L (S/N = 3), which was about 80-1090-folds lower than those of conventional sample injections. Linear response range were in the range of 2.5 x 10(-8)-2.0 x 10(-6)mol/L with the correlation coefficient between 0.9965 and 0.9994. Baseline separation was achieved within 10 min. After validation, the developed method was applied to determine 4-methylaniline, 3,4-dichloroaniline, 4-chloroaniline, and 4-aminophenyl in river water sample with average recoveries of 79.6-88.7%.