Abstract: The Zibo syncline basin geothermal field is a typical medium-deep hydrothermal karst geothermal reservoir area in North China, possessing abundant geothermal resources. However, a long-standing lack of in-depth research on the heat source, water circulation process, and thermal formation mechanism of this geothermal field has constrained its scientific exploration and development. Based on the actual investigation of geothermal wells, a total of 15 groups of karst hot water and cold water samples were collected in the study area. Through systematic analysis of conventional elements, hydrogen and oxygen isotopes, carbon isotopes, gas isotopes and hydrochemical characteristics, the heat source, channel, water source and circulation mechanism of geothermal water were revealed. The results indicate that: (1) The heat source of the Zibo syncline basin geothermal field has obvious crustal source dominant characteristics, mainly derived from the heat accumulation controlled by the normal geothermal gradient of the earth's interior during the deep groundwater circulation; (2) The fracture structure system governs the deep heat source and water sources; (3) Hydrogen and oxygen isotope tracing indicates that the recharge source of geothermal water is atmospheric precipitation; (4) Hydrochemical characteristics exhibit distinct geochemical zonation along the recharge-runoff-discharge pathway, indicating that the formation mechanism of karst hot water involves atmospheric precipitation infiltration, followed by evolution of karst cold water into hot water through deep circulation and confined stagnation under coupled tectonic-hydrogeological controls. Based on this, a “structure control–deep circulation–confined water stagnation” composite cause model is proposed; (5) The karst hot water in this area exhibits strong recharge capacity and, under reinjection conditions, can largely support sustainable development.