Abstract: The sample (50.0 mL) was adjusted pH to 3.0 with HCl solution, and adsorbed by swirling for 20 min with 50.0 mg of magnetic nanomaterials modified with ketopyrrolidine and divinylbenzene. After elution with 3.0 mL of acetonitrile, the eluent was centrifuged for 5 min, and filtered through 0.22 μm organic filter membrane. The filtrate was dried by N₂-blowing, and made up its volume to 1 mL, with a mixture of methanol-0.1% (φ) formic acid (60+40). The sample solution was separated by UHPLC using XDB-C₁₈ reversed-phase chromatographic column as stationary phase, and mixtures of methanol and 0.1% (φ) formic acid solution in various volumic ratios as mobile phase in gradient elution. MRM was adopted in MS. Linear relationships between values of peak area and mass concentration of 4 pheulurea herbicides were found in the range of 0.05-5.0 μg·L^-1, with detection limits (3.143s) in the range of 12.5-16.4 ng·L^-1. Test for recovery was made by standard addition method, giving results in the range of 83.7%-107%, with RSDs (n=6) all less than 8.5%.