By means of inorganic and organic chemical analysis, controlled source audio magnetotelluric sounding, high density resistivity and radon gas measurements, this study carried out detailed geological investigation for six ancient wellsin Jiuli village, DanyangCity, Jiangsu Province. The six well with interval spaces ranging from 30 to 200 cm have been boiling for more than 2000 years.The study found that (1) boiling gas in “boiling well” is mainly CO2, accompanied by a trace amount of radon gas and total volatile organic compounds (TVOC). All of the gas components in the “boiling well” have not been detected in nearby civil wells. (2) The contents of free carbon dioxide, calcium, iron, manganese, total dissolved solids, total hardness, bicarbonate, rare earth element etc. in “boiling well” water samples are significantly higher than that of other civil wells and lake water around the boiling wells. (3) The temperature of the well water in “boiling well” (about 19 degrees Celsius in summer) is basically the same as that of other civilian wells, with no anomaly observed. (4) The secondary faults of Maodong fault and basalt rock mass occur beneath the boiling well, and the concentrations of radon escaped to surface from the fault are significantly higher than that in other areas. (5) The existence of “boiling well” is closely related to the Maodong active fault. The boiling gas in “boiling well” comesmainly from deep crust or upper mantle, with the gas rising up along the fault zone to the earth surface. (6) The water in the six “boiling wells” tastes different because of the various contents of free carbon dioxide, calcium, iron, manganese and pHvalues. “Three clear three turbidity” features of the “boiling well” well water are closely related to ironcontent in wells. Three wells with high Fe contents are characteristic of turbid water and this may attribute to precipitation of ferric iron due to oxidation when water is exposed to air.