Abstract: The Chenjiazhuang buried-hill geothermal field is an important carbonate karst geothermal reservoir area in Shandong Province. The evolution of the geothermal field under large-scale production-reinjection conditions remains unclear, and there is a particular lack of criteria for determining the sustainable exploitation resource threshold. Numerical simulation is performed to determine sustainable exploitation thresholds under the dual constraints of thermal breakthrough and water-level safety, covering critical production-reinjection rate, critical well spacing, and recoverable resource amount. Based on regional structural and stratigraphic conditions, measured geothermal gradients, terrestrial heat flow, and full-hole temperature logging data, the main controlling factors of geothermal anomalies are systematically analyzed. A three-dimensional hydrothermal coupling numerical model is established using COMSOL Multiphysics. Under balanced production-reinjection constraints, multiple groups of production-reinjection parameters and well layout schemes are designed to simulate the long-term evolution of temperature and hydrodynamic fields in both doublet and multi-well systems, and the sustainable recoverable geothermal resources are quantitatively calculated to determine the threshold. The results show that: Low-temperature reinjected geothermal water accumulates around reinjection wells and forms a cold front that migrates toward production wells driven by density differences, water-level potential differences, and hydrothermal convection within the reservoir. In the doublet system, the thermal breakthrough time t of production wells decreases in a power function with the increase of production-reinjection rate Q, expressed as t=4819Q^−1.06, R²=0.9997. It increases exponentially with the rise of well spacing R₀, with the fitting formula t_\rmR = a\rme^bR_0 , where a and b are constants. R² > 0.97. Within a 100-year production-reinjection period, under the dual constraints of thermal breakthrough (average reservoir temperature drop ≤1 ℃) and maximum water table burial depth (D_max≤170 m), the sustainable exploitation threshold is determined as a well spacing of 600 m and a single-well production-reinjection rate of 80 m³/h, which are the critical safe production-reinjection parameters. Multi-well simulations show that the checkerboard well pattern forms a relatively uniform flow field, with an average reservoir temperature drop of only 0.47 ℃ and a maximum water table burial depth of 159.08–169.41 m over 100 years, meeting both constraints; the orbital pattern results in an uneven flow field and a higher thermal breakthrough risk; the centralized pattern causes severe imbalance of the geothermal field and has the poorest sustainability. Based on the checkerboard layout, a total of 144 production-reinjection well pairs can be theoretically deployed in the whole area. The calculated recoverable geothermal water yield is 27.65×10⁴ m³/d, the annual recoverable geothermal energy is 57.11×10¹⁴ J/a, equivalent to 19.49×10⁴ t/a of standard coal, which represents the resource threshold for sustainable exploitation. The findings provide a theoretical basis for the design of production-reinjection well networks and resource assessment in similar karst reservoirs with buried-hill settings, and also offer a reference method for determining sustainable exploitation thresholds in comparable geothermal fields.