Recently, more attention is paid to Synchronous Condenser (SC) as the problem of “strong DC and weak AC” is becoming increasingly serious. 300 Mvar SC will be put into service soon, which may affect the normal operation of the system relay protection. This paper analyses the impact of the SC access on the operation of Loss of Excitation (LOE) relay. A single machine infinite bus system model with SC is established in PSCAD/EMTDC and the operation of LOE protection under different generator loadings and different LOE modes is simulated. The simulation results show that the installation of the SC has adverse impacts on the LOE relay in the form of delay time and/or under-reach phenomenon, which is bound to threaten the security of generators. This work is supported by Key Project of Smart Grid Technology and Equipment of National Key Research and Development Plan of China (No. 2016YBF0900600).