In order to ensure the accuracy of the temperature measurement, it is necessary to perform cold junction compensation on the thermocouple circuit. At present, when using AD590 to perform cold junction compensation for thermocouple temperature measurement, there are problems such as circuit asymmetry and low safety. This design is optimized for the cold junction compensation of the S-type thermocouple. The thermocouple input circuit is separated from the AD590 cold junction compensation circuit. The output voltage of the cold junction compensation circuit is used as the bias voltage to superimpose the thermocouple signal, and the superimposed signal Perform amplification, filtering and other conditioning. The test results show that the common mode rejection ratio of the optimized circuit is increased by about 50dB, and the cold junction compensation accuracy is controlled within ±0.20FS, which can improve the symmetry and safety of the thermocouple input circuit.