The reliability of thermocouples with separation measuring junction in temperature measurement in the cooling process of hot steel plates with impingement jet has been investigated using direct and inverse finite element analysis (FEA). It is concluded that while the attachment of thermocouple wires on surface has negligible influence on surface temperature distribution during air cooling, the conduction of wires in a jet impingement water cooling process has significant effect on the measured temperature. The disturbance of the temperature field due to the introduction of a small hole for the installation of internal thermocouple has also been studied and showed similar but less pronounced effects to those of the surface measurement. An increased distortion of the temperature field is evident when the thermocouple is attached on the top surface directly above the bottom surface of hole.