For the image segmentation effect is not ideal in capsule defect detection, a segmentation algorithm of capsule image based on region feature is proposed. First, the original image is divided into 5 sub images, and then capsules are extracted from sub images. First of all, sub-image is removed highlight and noise, then put each row of image region as a sub-region, according to the characteristics of the capsule position in image region, find the boundary of capsule and non-capsule region and remove non-capsule region by judging whether exist boundary points between chain plate and background or not and whether capsule is connected with sprocket or not. Finally the capsule is extracted from sub-image after scanning the sub-image region line by line. Experiments show that the algorithm is fast and its accuracy and robustness are improved noticeably.