Abstract: A method for determination of 4 arsenic species, including, As(Ⅲ), DMA, MMA and As(Ⅴ), in surface water and sewage was developed based on self-developed combined instrument of high performance liquid chromatography (HPLC)-inductively coupled plasma mass spectrometry (ICP-MS). Sample of water was filtered by 0.45 μm filter membrane, and the 4 arsenic species were adsorbed with Agilent G3154-65001 chromatographic column as stationary phase, and eluted isocratically by a mixture solution (pH 6) composed of NaH₂PO₃ and Na₂EDTA as mobile phase. Targets obtained were detected by ICP-MS, and the collision reaction mode was used to eliminate the interference of ⁷⁵ArCl⁺ to ⁷⁵As. The results showed that As(Ⅲ), DMA, MMA and As(Ⅴ) could be separated within 7 min, and linearity ralationships between mass concentrations of 4 arsenic species response values were kept in the same range of 0.1-10.0 μg·L^-1, with detection limits (3.143s) of 0.34, 0.18, 0.11, 0.17 μg·L^-1, respectively. Test for recovery was made by standard addition method on actual samples, giving values of recovery in the range of 91.8%-110% and RSDs of the determined values less than 6.0%. As(Ⅴ) was detected in 2 water samples, and its content was lower than the limit (50 μg·L^-1) of GB 3838-2002. The proposed method was compared with related reference methods, and results of mtehod verification were basically at the same level.