Nowadays, gas-insulated transmission line (GIL) is playing an increasingly important role in the field of power transmission. It combines the advantages of cable and overhead transmission line, featuring with superior transmission performance and great potential application value. However, due to its own structural instability and other characteristics, it is easy to produce a series of faults, which seriously affects its transmission performance and safety performance. Therefore, this paper reviews some common monitoring methods for GIL. Firstly, it introduces the structure of GIL as well as its own characteristics and advantages, and then, according to the category of faults monitored in the monitoring process, the monitoring methods of GIL are divided into three major categories, which are the monitoring methods for partial discharge faults, structural defects faults, and overheating faults, and each category of methods is outlined and analyzed. Meanwhile, the specific application environment and implementation methods are analyzed. Each type of method is outlined and analyzed, and its specific application environment and implementation method are analysed. Secondly, the technical challenges faced by the monitoring of the transmission system of GIL are discussed. Finally, the potential future development trend of the proposed method is outlooked.