Abstract: In order to recognize regular slub yarn’s apparent parameters, slub yarn which was uniformly wound on black board was scanned and the grayscale and binary image of it was obtained. The digital image processing technology was used to rotate image and connect yarn on both sides in order to composite a continuous slub yarn image. Taking advantage of the correlation of periodic functions based on reading diameters of slub yarn, apparent parameter change period of slub yarn was determined. Based on analysis of the frequency of slub yarn’s diameter in several change periods, the diameters of the basic part and the slub part of the yarn were determined. By further analyzing the length of sections of certain amount of slub yarns appeared periodically, demarcation positions between basic part and slub part were found, thus the length of each basic part and each slub part was obtained and complete slub yarn’s apparent parameters were given.