Abstract: The triazine herbicides in seawater were determined by solid phase extraction ultra performance liquid chromatography with electrospray ionization tandem mass spectrometry(UPLC-ESI-MS/MS). UPLC and MS/MS analytical conditions were examined and optimized critically by a series of experiments. Samples were filtrated and purified on the HLB solid phase extraction cartridges. The elution was collected and evaporated to less than 1 mL at 40 ℃ by nitrogen blow, then added to 1 mL acetonitrile and water (1∶1，V/V) and ultrasonic wave extraction for 1 min. After filtrated with 0.22 μm filter membrane, the residue was separated by Acquity^TMUPLC HSS C18 column (2.1 mm×100 mm×1.8 μm) using gradient elution separation. The mobile phase was a mixture of A (acetonitrile) and B (5 mmol/L ammonium acetate containing 0.1% formic acid) in a flow rate of 0.25 mL/min. Finally analytes were confirmed and quantified using MS/MS system in multiple reaction mode with triple quadrapole analyzer using positive polarity mode. The analytes show good linearity in the range of 1 ng/L to 50 ng/L with correlation coefficient from 0.992 to 0.999. The detection limit is 1 ng/L，and quantification limit is 2 ng/L. The average recoveries at three dose levels(2 ng/L, 5 ng/L and 10 ng/L) are 65.8%—103% with relative standard deviations from 4.84% to 15.2%. In addition, the method has merits of simplicity, sensitivity and rapidity, and can be used for simultaneous determination of triazine herbicides in seawater.