Abstract：High iodine water is harmful to human health. High iodine groundwater is distributed around arid and semi arid inland basins, fluvial plains and coastal areas, which cover 12 provinces and autonomous regions in China. Huanghuaihai plain is a major region of high iodine groundwater. This paper points out that the source of iodine in groundwater is derived from the sea and brought in through atmosphere cycle, so iodine in the coastal aquifer, such as coastal aquifer of Huabei plain and that of Huaihe river plain, is usually high. The aquifer composed of alluvial and lake deposited materials with rich organic matter, ferric oxide and aluminum oxide often has high iodine, and the weathering crust of limestone possesses strong adsorption capacity for iodine. At last, this paper gives some suggestions for modification of iodine indexes in Groundwater Quality Standard（GB/T14848-93）》of China.