Abstract: A combined exploration & production well was drilled successfully in Wanxichong valley, in the periphery of Kunming geothermal field. The depth of the well is 2 001.6 m, the water temperature at the well head is 55 ℃, and the pumping rate of the well is 1 230 m3/d. Through the drilling study, the following formation rules of the sedimentary geothermal reservoir in Yunnan province can be summarized. Firstly, for areas where the depth of the carbonate rock strata is large enough, and areas where the temperature of the thermal water is estimated to be higher than 45 ℃according to geothermal gradient in the carbonate rock, these areas can be target areas for constructing geothermal wells, especially in faulted karst basins. Secondly, the distribution of carbonate rock strata in Upper Sinian Series Dengying Formation and Lower Cambrian Series Yuhucun Formation is very stable and the unconformable surfaces, faults and fracture structures in these carbonate rock strata form the major channels of the deep confined thermal water, resulting in the development of deep buried karst in the carbonate rock strata. Therefore, these carbonate rock strata have been common thermal water aquifers. Based on the abovementioned rules and the geological and hydrogeological investigation, it is advised that the southeastern boundary of Kunming geothermal field can be extended from Wujiaying Village of Chenggong County to the southern side of Jincheng Town for around 20 km.