As a large central city power grid, Guangzhou power grid requires high reliability of power supply. Three kinds of security and stability risks of Guangzhou power grid which may cause large-area blackout, as well as their corresponding strategies, are presented. A controlled islanding strategy for transient angle instability risk is proposed in case that the multi-circuit HVDC blocks at the same time and the out-of-step islanding devices fail to operate. The load-shedding strategy for the frequency instability risks of isolated local power grid is proposed in case that the entire 500 kV substation lays off. The generator splitting strategy for transient angle instability risk of local power grid is proposed in case of the main protection operation-failure under three-phase short-circuit fault. Simulation of real power grid confirms the validity of proposed strategies.