Abstract: Metal ions of the water containing boric acid are usually detected by atomic absorption spectroscopy and inductively coupled plasma optical emission spectrometer in nuclear power plants. Under the existence of the boric acid in water, the metal ion recovery rate and accuracy are significantly affected by boric acid with the method of atomic absorption spectroscopy. The limit of detection of inductively coupled plasma optical emission spectrometer is not enough to meet the need of trace metal ions in nuclear power plants. In this study, using the selective permeability of ion exchange membranes of suppressor to remove boric acid online, the metal ions were accurately determined by ion chromatography. The recovery rates of standard addition, relative standard deviations and method detection limits of Li⁺, Na⁺, K⁺, Mg²⁺ and Ca²⁺ are 97.0%-102.3%, 0.54%-1.25% (n=7) and 2.58-40.38 ng/L respectively, which demonstrates that this method can be applied in the analysis of Li⁺, Na⁺, K⁺, Mg²⁺ and Ca²⁺ concentrations in nuclear power plants. This method has the advantage of easy operation, reliability, fast speed and low detection limits.