A method in combination with derivatization-supercritical fluid extraction (SFE) and gas chromatography (GC) for the speciation and quantitative determination of dimethylarsinate (DMA), monomethylarsonate (MMA) and inorganic arsenic in solid matrices was investigated. Thioglycolic acid methyl ester (TGM) and thioglycolic acid ethyl ester (TGE) were evaluated as derivatization reagents. The effects of pressure, temperature, flow rate of supercritical CO2, extraction time, modifier and microemulsion on the efficiency of extraction were systematically investigated. The procedure was applied to the analysis of real soil and sediment samples. Results showed that TGE was more effective for arsenic speciation as a derivatization reagent. Modifying supercritical CO2 with methanol can greatly improve the extraction efficiency. Further, the addition of microemulsion containing surfactant Triton X-100 can further enhance recoveries of arsenic species. The optimum extraction conditions were 100℃, 30 MPa, 10 min static and 25 min dynamic extraction with 5% (v/v) methanol, and surfactant modified supercritical CO2. Detection limits in solid matriceswere 0.15, 0.3 and 1.2 mg/kg for DMA,MMAand inorganic arsenic, respectively. The method was validated by the recovery data. The resulting method was fast, easy to perform and selective in the extraction and detection of various arsenic species in solid matrices.