The high uncertainty in the thickness measurement of post irradiation sheet was analyzed, and based on the analysis, a large number of measurement tests were taken, a series of improvements were proposed. The manipulator driving measurement was replaced with the action-oriented measurement, which has effectively solved the problems concerning the stick side determination, the standard block fixing and the control of the head contact forces. The measurement uncertainty was reduced by one order of magnitude. The radiation dose, the labor tension and the time were likewise reduced with very significant economic and social benefits.