Synchronous condensers have gradually become the optimal choice for reactive power compensation equipment in DC ultra-high voltage（UHVDC）transmission systems due to their excellent reactive power response capability. During the use of the new synchronous condenser, various faults will inevitably occur, such as winding inter-turn short circuit fault, rotor eccentricity fault and bearing fault. But there is still little references on fault diagnosis technology for synchronous condensers. Therefore, the causes, fault characteristics and diagnosis methods of stator winding inter-turn short circuit fault, rotor winding inter-turn short circuit fault, rotor eccentricity fault, waterway blockage fault and bearing fault of synchronous condenser are summarized, and the characteristics of various fault diagnosis methods are analyzed. The challenges and development trends in the field of fault diagnosis for synchronous condensers are pointed out.