Abstract: To the water samples, after collection, 5 mL of 1.0 mol·L^-1 HNO₃ solution was added immediately for every liter of the sample, which should be then stored at 4℃. 9.0 mL of the sample was taken and mixed with 1.0 mL of a mixed solution of formic acid and acetonitrile (1+99). The solution was filtered through 0.2 μm filtering membrane, and the filtrate was passed through Shim-pack XR-ODS Ⅱ chromatographic column and eluted with the mobile phase of mixed solution of 0.1% (φ) formic acid solution and acetonitrile (3+7) to separate carbofuran (CF) from other co-existing impurities. The eluate was pumped to the ionic source of MS/MS under optimized condition, and under the mode of ESI⁺, the ion of quasi-molecule of CF,M+H⁺ m/z 222.2, was fragmented to 2 main fragmented ions of m/z 123.0 and m/z 165.1. Ratio of peak strengths of these 2 ions was I_{m/z 123.0}:I_{m/z 165.1}=100:20. In latter testings, the ion-pairs of m/z 222.2/123.0 and m/z 222.2/165.1 were used for qualitative analysis, and the former ion pair was used for quantitative analysis. The proposed pathway of fragmentation of CF was confirmed by Q Exactive HRMS. In the analysis of water samples, based on the data of retention time (2.67 min) and fragmented ions, as well as the ratio of the peak strengths, as given by the analyte, and by comparing with the data given by standard solution of CF, the presence or not of CF in the sample could be concluded. As shown by results of quantitative testing, linear relationship was obtained between values of peak area and mass concentration of CF in the range of 0.05 to 10.0 μg·L^-1, with detection limit (3S/N) of 0.01 μg·L^-1. Values of recovery found by standard addition method ranged from 88.4% to 96.5%, and values of inner-day RSDs (n=6) and inter-day RSDs (n=6) were in the ranges of 0.90%-5.6% and 1.8%-7.3% respectively.