Abstract: Metsulfuron-methyl and bensulfuron-methyl in paddyfield water were determined by ultra performance liquid chromatography-tandem mass spectrometry（UPLCMS/MS）. The remains of metsulfuron-methyl and bensulfuronmethyl were extracted with solid phase extraction C₁₈ cartridge.The separation of metsulfuron-methyl and bensulfuron-methyl was performed on Waters Acquity UPLC system with a BEH C₁₈ column (50 mm×2.1 mm×1.7 μm) and with a linear gradient elution (CH₃OH and 0.05% acetic acid as mobile phase) at a flow rate of 0.4 mL/min， and detected by MS/MS with positive electrospray ionization mode. The method used external standard for quantification. The calibration curves have good linear correlation in the concentration range of 1.0—500 μg/L（r=0.999 7—0.999 9）. The limits of detection are 0.002 5 μg/L and 0.005 μg/L，respectively. The recovery is in the range of 87.6%—98.2%, and the RSD is less than 3.5%．