Aiming at the transmission line insulator images obtained by drones or robots, this paper proposes an online recognition and defect diagnosis model of Cylinder Head transmission line insulators based on YOLOv2 network.The YOLOv2 network is trained to learn and accurately recognize the characteristics of various insulators under complicated background, and eventually to accomplish the defect diagnosis of the identified insulators of various status by means of edge detection, line detection, image rotation and vertical projection methods.The simulation results of the patrol inspection images of the transmission lines show that the proposed automatic insulator identification and defect diagnosis method can quickly and accurately identify the insulators from the patrol images of the transmission lines and diagnose the defects and their locations of the insulators, which is beneficial to Scales and Body Composition Analyzers - Scales enhance the intelligence inspection level of transmission lines.