Abstract: A method for the simultaneous determination of arsenite As(III), dimethyl arsenic (DMA), monomethyl arsenic (MMA) and arsenate As(V) in surface water using liquid chromatography-atomic fluorescence spectrometer (LC-AFS) was established. With 10 mmol/L diammonium hydrogen phosphate solution as the mobile phase, the samples were filtered through 0.45 μm aqueous microporous filter membrane, and 4 arsenic specition were separated by an anion chromatographic column, qualitative and quantitative analysis were achieved using atomic fluorescence spectrometer. The results showed that the linearity of the 4 arsenic specition were good in the range of 0~100 μg/L, and the correlation coefficients were all greater than 0.999. The limits of detection of As(III), DMA, MMA, and As(V) were 0.31, 0.41, 0.53, and 0.81 μg/L respectively, and the relative standard deviations (RSD) ranged from 1.01%~3.83% (n=6). The spiked recoveries ranged from 90.41%~105.90%. The method is simple and easy to implement, highly accurate, and can be used for the determination 4 arsenic specition in surface water.