Abstract: The thermal reservoir above 4 000 m depth is the research object in this paper. Through summarizing the characteristics and exploration situation of the geothermal resources in Tianjin, the authors utilized the thermal reservoir method combined with water balance method and numerical coupling optimization management model method to calculate the 30 years’ resource quantities and exploitable heat of the main thermal reservoir in Tianjin. The results show that by the end of 2045, according to the water balance method,the exploitable resource quantities and heat are 27.012×10¹⁸m³ and 47.0×10¹⁶J respectively, and according to the numerical coupling optimization management model method, the exploitable resource quantities and heat are 26.6×10¹⁸m³ and 49.74×10¹⁶J respectively. The results of the two methods are basically consistent. This could provide some reference for rational development, utilization and management of geothermal resources in Tianjin.