Optimizing the production and reinjection parameters of a “doublet” system is of significant importance for the sustainable development and utilization of geothermal resources in sandstone thermal reservoirs. This system, consisting of a closed loop with one production well and one reinjection well, plays a vital role in the temperature recovery of reinjected cooled geothermal water. In this research paper, we establish a hydro- thermal coupling numerical model for the “doublet” system based on the long- term hydrodynamic and geo- temperature monitoring data from the production and reinjection wells at the Guantao Formation thermal reservoir. Our study focuses on understanding the evolution and trend of the temperature field in the thermal reservoir caused by reinjected cooled geothermal water. Additionally, we aim to optimize the key parameters of both the existing and planned “doublet” systems. Furthermore, we investigate the heat sources contributing to the temperature recovery of the reinjected cooled geothermal water and provide a quantitative calculation. The findings reveal that the basal conglomerate at the bottom of the Guantao Formation reservoir, with its high permeability, exhibits the fastest migration rate for reinjected cooled geothermal water. To ensure the absence of thermal breakthrough in the production well of a typical “doublet” system within 100 years of operation, the production and reinjection flow rate Q should not exceed 30 m3/h. When the production and reinjection flow rate Q of the proposed “doublet” system is designed with a conventional value of 72 m3/h, the reasonable distance R between the production and reinjection wells should not be less than 300 m. The thermal breakthrough time t in the production well increases as a power function with the increase in the distance R, as described by the correlation equation tQ=aR2. 4. Examining the heat sources contributing to the temperature recovery of reinjection cooled geothermal water, the analysis indicates that the convection heat between the reinjection cooled geothermal water and its peripheral hot geothermal water in the same layer is the source of heat recovery with the largest proportion, accounting for more than 70% at the beginning of reinjection and remaining at 36.0% after 100 years of reinjection. The proportion of conduction heat absorbed by cold water from the roof and floor of the reservoir increases from nearly 0% to 30. 7% (roof: 11. 5%, floor: 19. 2%) in 100 years of reinjection. The proportion of conduction heat in the same layer absorbed by the reinjected cold water from the peripheral heat reservoir media increases rapidly from nearly 0% to 13. 5% and then stabilizes. The proportion of heat absorbed by the cooled geothermal water from the internal reservoir medium gradually decreased from 25.4% at the beginning of reinjection to 19. 8% at 100 years of reinjection.