To extract the edge information of noisy Printed Circuit Board (PCB) defect image, an image edge detection method based on mixed method was proposed. The basic principle and advantages of the image segmentation method based on the Maximum Distance Between Categories (MDBC) were analyzed, and its improved segmentation method (IMDBC) was proposed. The image edge detection method based on the mixed method by combining with median filter, IMDBC, the improved mathematical morphology edge detection operator and LOG operator was discussed. The edge information extraction experiment by using four PCB defect images acquired by CCD and microscope imaging system was carried out. The experiment results show that it can extract better the PCB defect image edge information by using this method, and it has lesser noise points. In this method, the image excellent quality coefficients are from 1.0111 to 1.3586 times of other six methods mentioned in this paper.