An embodiment of the invention provides a method and device for detecting power transmission line defects and relates to the field of power component detection. By the method and device for detecting the power transmission line defects, the judging accuracy of the power transmission line defects can be increased. According to the technical scheme, the method includes: determining a feature extractor, which is a mapping function between an infrared image and the data feature of the infrared image, through unsupervised learning; acquiring a target infrared image, and extracting the data feature of the target infrared image through the feature extractor, wherein the target infrared image is the infrared image of a power transmission line; using a classifier to perform classification detection on the data feature of the target infrared image so as to identify the positive sample of the target infrared image, wherein the positive sample is the infrared image sample of a power component on the power transmission line; performing temperature analysis on the positive sample, and outputting a defect judging result.