Aiming at the problems existing in relay protection and secondary loop in practical application, the author analyzes the current status of power system relay protection and secondary loop, and forecasts its development direction. According to the working principle of the secondary loop, using modern technology, combined with the current situation of relay protection and secondary loop in China, this paper puts forward the development of relay protection technology towards integration of intelligence, network, protection, control, measurement and communication. The trend of secondary loop towards comprehensive automation is discussed, and the application of new technologies in the field of relay protection and secondary loops is described separately. The results show that the research has certain practical reference value.