Abstract: A new complex chemiluminescence system, i.e., luminol H₂O₂ catalyzed by CoHR^- complex is reported. Based on this catalyse a new chemliuminescence method for determining trace of Co(Ⅱ) is proposed. The detection limit is 1.29×10⁹ g/L Co(Ⅱ), the linear dynamic range is 5×10⁸-1×10⁵ g/L Co(Ⅱ) and the variation coefficient at a cabalt concentration of 1×10⁷ g/L Co(Ⅱ) is 2.5% (n=5). This mettod has been applied satisfactorily in the determination of trace cabalt in waste waters.