A large number of aerial images are generated in the inspection of transmission lines. Due to the different sizes of conductors, insulators, shock absorbers and other components, the problem of rejection is easy to occur in the detection of external damage hazards, which affects the overall identification effect of lines. In this paper, a method to identify the hidden danger of external damage of high voltage overhead transmission lines is designed. From the three aspects of color, texture and shape, multi feature extraction is carried out on the line image to represent the location information of external damage hazards. The line image to be recognized is divided into uniform grids, and the coordinates and confidence of sub image blocks are used. Calculate the prediction accuracy of each region, filter the sub region with the largest value as the candidate target region, and output the corresponding prediction box. The deep transfer learning model is used to identify the hidden danger of external damage of the line, and the difference measurement index is used to evaluate the input feature vector. The difference feature results are fed back to the convolution layer to strengthen the interpretation ability of the difference information. The test results show that the design method improves the ability of image feature extraction, has high recognition accuracy, and provides decision-making basis for intelligent line early warning.