Abstract: Based on image processing and pattern recognition, this paper studied the automatic recognition module of EMU brake pad thickness to solve the problem of rapid wheel temperature rise and even unsafe state caused by too thin brake pad during EMU braking. The module could implement the automatic detection of EMU passing: automatic jigsaw puzzle, image preprocessing, model positioning and brake pad thickness calculation, and automatically alarm the brake pad whose thickness was less than a certain value. A large number of experiments and tests show that the module can calculate the thickness of the brake pad effectively and has good robustness.