The invention relates to the technical field of generators and auxiliary systems, and provides a low-voltage protection system of a megawatt-level nuclear power plant. The low-voltage protection relaymodule is connected with a generator control loop and is used for receiving control signals to control the on-off of the generator control loop. Wherein the control signal is triggered simultaneouslyby a plurality of different switching signals, the plurality of different switching signals comprising a low-voltage protection switching signal; A low-voltage protection control module is connectedwith the bus bar of the distribution system, and is used for output a low-voltage protection switch signal, wherein the low-voltage protection switch signal comprises an open signal and a closed signal; The low voltage protection control module is configured to maintain an output disconnect signal when the low voltage protection control module fails or the low voltage protection control module ispowered off. The output closure signal is maintained when the bus voltage of the distribution system is lower than the set value. It effectively avoids the malfunction of generator low-voltage protection when the low-voltage protection control module fails or the power is cut off in the megawatt-class nuclear power plant.