The frequent occurrence of transmission line galloping induced by wind deflection poses a serious threat to the stable operation of power systems and results in significant economic losses. Therefore, the real-time online monitoring of transmission line galloping has become a key focus of research. This paper reviews the causes of transmission line galloping and discusses the current online monitoring technologies and system performance. Commonly used monitoring methods, and existing limitations are analyzed, and the major challenges faced by current galloping monitoring technologies are summarized. To address these challenges, a fusion monitoring method combining MEMS vibration sensing and BeiDou (BD) differential positioning is proposed. By integrating WSN/GPRS/BD communication networks, a real-time online monitoring platform for large-span transmission lines is established. This platform, which unifies sky, ground and space communication through the Beidou system, enables accurate real-time monitoring of transmission line galloping. The proposed approach provides valuable guidance for the real-time online galloping monitoring technologies for transmission lines.