Abstract: With the large-scale application of precision thermometers with a temperature measurement accuracy of up to 1 mK or even 0.1 mK in experimental equipment and aerospace equipment, higher requirements are placed on the temperature control accuracy of the thermostatic bath used in the traceability of precision temperature measurement values. A thermostatic bath with a temperature control accuracy of less than 1/10,000 to meet the traceability requirements of its value. In this paper, the model of the thermostatic bath for testing precision thermometers is built by using the thermostatic calorimeter temperature control mode, and through theoretical analysis and experimental verification, the thermostatic bath model can meet the calibration requirements of precision thermometers with a temperature measurement accuracy of 1 mK or even 0.1 mK.