Abstract: Transmission line fittings are important components for mechanical connection, fixation and protection on transmission lines. They are prone to defects, such as damage, rust and contamination, due to the complex climatic conditions and harsh natural environment. Unmanned aerial vehicles, artificial intelligence and other advanced technical means used to detect and eliminate the defects on transmission lines in time is the key to improve the maintenance efficiency and ensure the safe operation of transmission lines. This paper firstly divides the fittings and their defect types in detail according to the functions of the transmission line fittings, and summarizes the commonly used object detection methods based on deep learning and the methods for small fittings detection and occluded fittings detection based on deep learning. The research status of several key fittings and their defects detection methods are reviewed and analyzed. Finally, the problems and research directions for fittings detection are analyzed and discussed.