As the amount of AC/DC hybridization increases in power systems, the difficulty of grid operation has increased significantly. Therefore, ensuring the safe operation of AC/DC hybrid grid has become a major and urgent issue for China. The converter station is the hub of an AC/DC hybrid grid. Different from the traditional synchronous machine power supply, its fault coupling characteristics are complicated. In this paper, starting from the response and transfer characteristics of the converter station to the disturbance, this paper explains the coupling characteristics and generation mechanism first. This provides a theoretical basis for the fault analysis and protection research of the AC/DC hybrid grid. Furthermore, it evaluates the adaptability of AC and DC line protection and studies new principles of relay protection in different fault periods. Finally, it puts forward an idea for control and protection coordination, and discusses further research directions. This work is supported by the Joint Fund Key Project of National Natural Science Foundation of China (No. U1766209) and the Science and Technology Project of the Headquarters of State Grid Corporation of China (No. 52094020006U).