Abstract: This paper mainly presents how to improve the safety and reliability of generator loss-of-excitation protection of Tianwan nuclear power station,and the backward technology and poor reliability generator loss-of-excitation protection which was made in Russian had been transformed to microcomputer protection.A set of maintain effective experiences of designing,installation,commissioning and maintenance about generator loss-of-excitation protection is summarized.Practice has proved that it is of great advantage to enhance the operation reliability and safety of the generator,and shorten the maintenance period after the transformation of the generator loss-of-excitation protection.