Abstract：The study area is located in southwest Taiyuan basin of Shanxi Province. Totally 950 water samples were collected from the shallow wells (≤50 m), middle wells (50-200 m) and deep wells ≥200 m) . With ICP-MS and HPLC-ICP-MS methods, the authors determined the total iodine content and inorganic iodine content, which included iodine ion and iodine acid radical (I- and IO-3). The results indicate that the proportions of iodic concentration that exceeds the standard are 76.8%, 70.3% and 85.2％ in groundwater of three layers, respectively. The highest iodic concentration in the shallow groundwater is up to 4117μg/L, which is 27 times higher than the national standard of drinking water (150μg/L). The main form of iodine in the groundwater is ionized iodine, with small amounts of iodate. About 60% water samples have organic iodine. The main causes for high iodine concentration in groundwater are special topography and aquifers in the study area, which results in hindered movement of groundwater. Furthermore, local agricultural irrigation using the middle or deep layer groundwater and salinization of surface soils in the low-lying lands has led to the increase of iodine in the shallow layer groundwater. Iodic source in groundwater is closely related to geological environment of marine, lacustrine and fluvial sediments. The results could offer scientific means to reforming water projects in high iodic water areas of China.