Abstract: 0.3 mol/L phosphoric acid and 0.1 mol/L ascorbic acid were used to extract the sediment samples following a microwave-assisted extraction procedure. 2.0 mmol/L NaH₂PO₄/0.2 mmol/L EDTA (pH 6.0) were used as the mobile phase, to determine the concentration of As(Ⅲ), As(Ⅴ), MMA and DMA in the extracted liquid by high performance liquid chromatography-inductiuely coupled plasmamass spectrometry (HPLC-ICP-MS). The chromatographic peaks of 4 arsenic species are completely separated in 10 min. The linear correlations are satisfactory. The recoveries are between 94.2% and 110%. The extraction efficiency of arsenic species were 80.4%—98.7%. The results show that arsenic species in the surface sediments of Taihu Lake are mainly inorganic arsenic. And organic arsenic species are not detected. The content of As(Ⅴ) in the samples are higher than that of As(Ⅲ), which indicate that the surface sediments of Taihu Lake basically are in the oxidizing environment. In the recent 20 years, the arsenic content in the sediment of Taihu Lake had increased evidently. The arsenics were inorganic species in the vertical profiles of sediment, and there were no remarkable differences for the relative ratios of the arsenic species in each section.