Abstract: The measurement methods for dent depth on nuclear mechanical component were discussed during the installation and service of pressurized water reactors.The origins for the measurement errors in the welding inspection by calipers and moulding film were analyzed.Based on the measurement data from dents on the steam generator plate,the evaluation methods for the measurement uncertainty of the above two techniques were provided,and the uncertainty component was analyzed.The combined standard uncertainty was calculated.The calculated result indicated that the uncertainty of two methods come from the random uncertainty component of repeated measurement and system uncertainty component of system correction imperfection.