This paper discussed the three-defense-lines of security protection system. The three-defense-lines was expanded under the condition of using smart grid technology, based on the analysis of intelligence support technologies, such as intelligent power generation, substation, transmission, dispatch, communication and the wide area measurement. The technology of intelligent prevention and control could optimize the grid operation scheme with the methods of risk early warning and forecast verification, and made terminal of defense system effectively move forward. The technology of intelligent emergency control could implement the strategy of global closed-loop control with the methods of online calculation and real-time control, which could strengthen the stable operation of power grid. The technology of intelligent restoration control could speed up recovery process of power grid with the methods of default scheme and rolling optimization, which could effectively reduce blackout time and economic loss.