Abstract: The environmental sampling (ES) analysis is one of important nuclear safeguards’ technologies of International Atomic Energy Agency (IAEA), which has been used for detecting the undeclared nuclear activities. Plutonium is regarded as the significant element in nuclear safeguards. In the aspect of ES, bulk analysis is adept at the analysis of plutonium ratio in environmental samples. In this paper, the method of on-line analysis of plutonium ratio in water samples was established by combination of ion chromatography (IC) and multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). The separation conditions of liquid chromatographic column, the column acidity, eluent composition were optimized. The AS4A-SC anion chromatographic column was made sure as separation medium. The separation conditions in which the acidity of column was 7.5 mol/L and the eluent composition was 0.35 mol/L HNO₃ mixed with 0.01 mol/L HF were determined by optimization experiments. The concentrations of uranium in various types of environmental water samples were measured. The interface was determined in order to combine IC and MC-ICP-MS. The effect was confirmed better when using PEEK two way valve to connect IC and MC-ICP-MS. The technique of peek apex ratio was adapted as the method for the measurement of dynamic plutonium ratio by MC-ICP-MS. The simulated water samples were measured. The RSD is 0.50%, and the relative bias compared with the plutonium certified reference material is 5.7%. The actual water samples were also measured. The RSD is 0.97%, and the relative bias is 1.3% compared with the typical separation methods by TBP and 7402 chromatography column. This method has high efficiency and fast analytical speed, which can be used for the measurement of plutonium ratio in other environmental samples with more complicated matrices.