Abstract:A method to determine trivalent and pentavalent arsenic in groundwater by a combined liquid chromatography-atomic fluorescence spectroscopy (LC-AFS) was established based on the mobile phase of potassium dihydrogen phosphate and disodium hydrogen phosphate with the flow rate of 1.0 mL/mim .This approach achieved simultaneous analysis of As3+ and As5+ within 10 min. showing good linearity, low detection limit of 0.02μg/L, high degree of automation and excellent repeatability.