Abstract:X-ray thickness gauge made by Toshiba is the key testing equipment and an important part of automatic thickness control system (AGC) of X mill for copper foil rolling. It is the basic condition to ensure the effective and correct thickness control of the mill that the thickness gauge has the function of accurate thickness measurement. We analyze and study the mechanism of full calibration and precision verification based on the composition and measurement principle of thickness gauge. Effective measures are taken to improve the accuracy, stability and reliability of the thickness gauge in view of the failure of the standard plate falling off inside the standard changer and the deterioration of the X-ray generator.