The invention relates to an X-ray imaging stretching fault automatic detection method for a steel cable core conveying belt joint, which belongs to the field of X-ray nondestructive detection. Defects of lower reliability, poorer accuracy, non-visual display, dependence mainly on manual detection and the like exist in the current stretching fault detection of a current steel cable core conveying belt joint. The invention consists of the following three aspects: 1. on the basis of the gray level change characteristic of X-ray images of a steel cable core conveying belt, screening out images containing partial or all joint information from the X-ray images of the whole steel cable core conveying belt by adopting local histogram information; 2. splicing the screened images into the corresponding image containing the complete joint information; and 3. realizing the judgment for the stretching of each joint by adopting an improved condition Y-difference algorithm and a clustering method. The invention can automatically, rapidly and efficiently realize the stretching fault detection of the steel cable core conveying belt joint.