This paper proposes the ion chromatography (IC) with online pre-column filled with Styrene-DVB copolymer. The recoveries by this method are 96%~102% with a precision of 1.7%~2.9% and detection limits of 5.0~9.0 μg/L. The method is used to determine the concentrations of F^-, Cl^-, NO<SUB>3^-, SO₄^2- in the ground water and surface water near to the Chengdu University of Technology. The results show that the new method can remove acetic acid from the samples online, prolong the life time of analytical column, and overcome the shortcomings of the offline pretreatment.