A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS)method or perfluorooctane sulfonic acid (PFOS) analysis in water was established. The water sample was pretreated with a 0.22 μm PP filter membrane, and then 200 mL pretreated water was enriched with a Poly-Sery HLB solid phase extraction column. The enriched extraction column was eluted by passing it through 10% aqueous methanol, after which the elution chamber was evacuated and the column was washed again with 4 mL methanol. And then ACQ MITY MPLC BEH C₁₈ chromatographic column was used to separate the eluent in the negative ion multi-reaction monitoring mode detection, fragment ion m/z=80, by internal standard method quantitative analysis, using a 0.1% formic acid aqueous solution-methanol solution as mobile phase. Under preferred conditions, PFOS was linear in the concentration range 0.01-50 μg/L with a correlation coefficient r>0.99, and the method limit of detection was 0.25 μg/L. The spiked recoveries ranged from 82.1% to 104.5% and the relative standard deviations (RSD) ranged from 2.34% to 5.64% for PFOS at the spiked concentrations of 0.2, 2.0, and 20 μg/L, respectively. The PFOS content in the actual water samples was below the detection limit, the lake water spiked recovery rate was between 84.75%-112.2%, RSD<5.62%, and the aquaculture water sample spiked recovery rate was between 81.7%-118.6%, RSD<7.51%. The established method can accurately detect PFOS in environmental water.