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 IO3-). 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.