Abstract: The fracture zone in the southeast foothills of the Taihang Mountains is well developed and endowed with abundant medium- and low-temperature geothermal resources; however, the hydrothermal genesis pattern of deep geothermal water in this area remains unclear. Based on the hydrochemical composition characteristics of 55 geothermal water and 38 shallow groundwater, this study analyzed the source and migration law of ion components, and the recharge source of geothermal water leveraging isotope characteristics. On this basis, the water-rock equilibrium state, temperature, and depth of thermal cycle of deep thermal reservoirs were revealed. The results show that the study area is a convective-conducting composite geothermal system, and the geothermal waters as a whole are in an oxidizing environment, with the ionic fractions dominated by \mathrmHCO_3^- and Na⁺, which are mainly controlled by the dissolution of minerals, such as rock salt and carbonate, as well as by the cation exchange. Furthermore, the recharge elevation of the geothermal water ranges from 1 010 to 1 153 m, which indicates that the recharge area of the geothermal water is located in the western part of the Taihang Mountains. The depth of the circulation ranges from 1 125 to 4 468 m. The estimation of the mixing ratio method indicates that the temperature of the deep thermal storage of the Tangyin Rift reaches 110 to 160 °C, while that of the Neihuang Uplift is 80 to 110 °C. The difference in thermal reservoir temperature is caused by the good conditions of heat and water conductivity of Tangdong and Tangxi deep faults on both sides of the Tangyin fault, and the shallow buried depth of bedrock of the Neihuang Uplift with the thin overlying cap rock, which makes the heat energy more easily dissipated. The study reveals the geothermal hydrochemical characteristics and hydrothermal genesis model of the geothermal system at the southeastern foot of Taihang Mountain and provides a basis for the calculation and exploitation of thermal resources.