Abstract: In order to address the issue of measurement accuracy in the calibration of temperature itinerant detecting instruments, a new mathematical model has been established for measuring the low-temperature Pt100 sensors and high-temperature thermocouple sensors based on existing technical specifications. The GUM method has been employed to assess the measurement uncertainty of the temperature itinerant detecting instruments, which provides technical support for improving the traceability and transfer system of these instruments and revising the calibration specification. The results show that the GUM method identifies the primary sources of uncertainty as the temperature itinerant detecting instruments' indications and the performance of the constant temperature sources. The uncertainty of the low-temperature Pt100 sensors is 0.03℃ to 0.07℃ (k=2) in the range of -80℃ to 600℃, while the uncertainty of the high-temperature thermocouple sensors is 0.8℃ (k=2) in the range of 600℃ to 1000℃. Furthermore, the use of a salt bath tank can significantly improve the calibration accuracy of temperature sensors in the temperature range of 300℃ to 600℃.