Smart grid is a future self-healing power system which will combine with the novel control, information and management techniques, realize a series of intelligent interactive activities from power transmission to electricity end users, and optimize electricity generation, transmission and distribution scientifically and systematically. This paper analyzes features and recent progress of smart grid firstly. Then, based on the requirements of detection for high voltage transmission equipments as well as plans of smart grid construction in China, the importance of on-line monitoring techniques for smart grid are highlighted. Meanwhile, aiming at the difference of smart grid and traditional grid, it also presents some specific and step by step proposals for the realization of on-line monitoring of high voltage transmission equipments. It suggests that the future work should be focused on the high voltage equipment such as intelligent equipments development, reliability analysis and residual life estimation according to on-line monitoring data, life cycle management and accurate evaluation system, intelligent maintenance using expert systems and et al. Solution of the above problems will be helpful to deep research and application of smart grid.