Sinking columns are one of the most hazardous geological structures in north Chine typed coal fields.To understand the sinking column formation,to judge if the columns are hazardous or not,the inner circle mechanism of groundwater in forming sinking columns in the relatively isolated areas was proposed according to the investigation on formation or distribution of sinking columns in some north China typed coal fields.such as Fengfeng,Xiangtai,Huaibei,Yangquan and so on.The heat generated by magma energized groundwater circulation and developed limestone karst in the relatively isolated areas.The CaCO3 solution accelerated by geothermal abnormality,the effect of high content of CO2 on dissolution and saturation of CaCO3 were discussed.Compared the forming conditions of the sinking columns developed in other coal mining areas in north China coal field,the paper deduced that the above factors collude karst development and sinking column formation,the columns in current geothermaI areas are permeable and those in high coal rank areas or in paleo abnormally geothermal areas.The paper suggested that the sinking columns in the current abnormally geothermal areas were permeable,but those in the areas with high coal rank were not on contract.