In this article the laser diffraction technology is extended to a new application field to measure the thickness of 1.5-meter-wide soft graphite roll. The broad graphite roll in high quality has wide application, but its production process must have corresponding real-time and nondestruct ive measuring and observation system. Using low-power laser as illuminant, a se t of applicable metrology scheme that could measure both the thickness and the u niformity of graphite roll is advanced -- relative method is used to measure the thickness and multi-point measurement method is used to measure the uniformity . Some discussion on the selection of the related important parameters are also given here, and some modified measures concluded from experiments are proposed. What's more, the real-time processing on diffraction stripe is studied.