Abstract: Fenhe second reservoir of Shanxi Province is a medium-sized reservoir built in the middle and upper reaches of Fenhe river. Because the reservoir is located in the section of carbonate river which is the junction of the spring fields of Jinci and Lancun, the reservoir impounds and inundates the Xuanquansi spring group that flows out under natural conditions , resulting in a fundamental change in the karst hydrogeological conditions in the reservoir area. This directly affected the water resources evaluation, development and management and the measures planed for ecological restoration aimed at spring re-flow. This article discusses the following two issues related to the construction of Fenhe river second reservoir. First, using the latest survey and exploration data to analyze the impacts of the construction of the second reservoir on the karst-hydrogeological conditions and delimit the spring field in the second reservoir areas. It is believed that the outflow of Xuanquansi spring is controlled by the semi-aquitard of the lower Ordovician inclined to the west within the Fenhe river valley. The water level of the second reservoir has been elevated by nearly 40 m and filled the falling funnel in the Xuanquansi spring area which is a relatively independent circulation between the Jinci and the Lancun spring under natural conditions. The spring disappeared and it forms a reverse supply to the karst groundwater. The water seepage of the reservoir mainly flows into the Jinci spring domain through the middle Ordovician. The Fenhe second reservoir is bounded by the outcrop of the lower Ordovician between the Sitou and Xiahuai. The reservoir area above the Sitou-Xiahuai is assigned to Jinci spring field and the reservoir area below the Xiahuai is assigned to Lancun spring field. Second, by using the hydrological data of the reservoir's upstream and downstream and series of water level data of the second reservoir, a nonlinear relationship between the second reservoir's water level and the amount of seepage is established by the equilibrium method. Based on this, when the water level of the second reservoir rises to 905.7 m, the seepage amount would be 2.862 m3·s-1. However, the supply of Lancun spring karst water and Piedmont Xizhang source water is limited.