A HPLC-ICP-MS method for simultaneous determination of AsⅢ, AsⅤ, MMA and DMA in traditional Chinese medicines (TCMs) was established, and the contents of AsⅢ, AsⅤ, MMA and DMA in a TCM with high total arsenic content (Cordyceps) and 5 crude and processed TCMs (Radix Astragali, Radix et Rhizoma Rhei, Radix Scutellariae, Radix Polygoni Multiflori and Radix Rehmanniae) were determined and analyzed. The method validation indicated that the correlative coefficients (r) for all speciations were bigger than 0.998 4; the limits of quantitation (LOQ) were from 0.8 to 1.0 μg·L-1; the reproducibility and stability were satisfactory with all RSDs less than 10%; the spiked recoveries ranged from 82.40% to 119.5%. The results of samples analysis showed that the inorganic arsenic (AsⅢ and AsⅤ) was the dominating speciation in the tested TCMs; MMA and DMA were not found in all plant resourced TCMs, but MMA was found in Cordyceps; all the tested TCMs indicated a content increasing of inorganic arsenic after processing.