Abstract: There are many reports about endemic arseniasis in China. Jianan in Taiwan, Kuitun in Xinjiang, Hetao area in Inner Mongolia and Datong in Shanxi are four typical arseniasis areas. The arseniasis areas are mostly deposits of river and limnetic facies or marine bed with clay, clayey and organic mud, and belong to environment with rich organic matter. Arsenic in groundwater is 0.2-0.6 mg/L and some harmful organic materials, such as fluorine, humic acid, methyl arsenate and hydrocarbon. Arseniasis related mainly to total arsenic, As³⁺ and methyl arsenate. Besides arseniasis, there are fluorosis and cancer in these areas. Because of the difference of chemical compounds in ground water, there are different "dangerous concentration" and arseniasis types. Three geological environmental types are classified. The paper not only summarize the characteristics of geological environment but also provides important basis for prevention, cure and research of arseniasis.