Abstract: This paper introduces the types of on-line monitoring devices for overhead transmission lines, and the development of on-line monitoring technology in China.According to different application scenarios, the deployment principles of online monitoring devices are proposed.Under the background of power equipment IOT construction, new IOT sensors, edge intelligent terminals and other devices are constantly emerging.This paper analyze the functional requirements of the transmission line edge intelligent terminal, introduces the hardware architecture of the device and the software architecture of edge computing.This paper analyzes the shortcomings and bottlenecks in the development of online monitoring technology, discusses the development of advanced sensing technology for on-line monitoring, micro source energy extraction, wireless sensor network and other technologies.At last puts forward the direction and trend of technology development.