The existing security and stability control strategy is based on off-line calculated expected modes and failure set, and is difficult to comprehensively cover all special operation modes of the power grid. The existing transient instability criterions based on wide area response are analyzed and compared. By utilizing the coherent variation of power-angle of generator and voltage in oscillation center during the serious fault of the power system, a transient stability discriminant technology is presented considering the time integration of the oscillation center voltage trajectory. A transient stability online pre-detection control system based on wide area response is developed by adopting the centralized control structure scheme, and it can achieve fast and practical discrimination of the power system transient stability status without relying on model. The control system is successfully applied to the northern power grid of Liupanshui in Guizhou, and is operating normally so far to support emergency control during serious fault in power grid.