Transient stability control technology is one of the core problems of power system for maintaining security and preventing blackouts. With the development of wide-area measurement system (WAMS) based on phasor measuring units (PMU), the response-based transient stability control technology has become an important development direction. From a viewpoint of combining both theory and application, researches of wide-area protection are reviewed on three important subproblems. They are perturbed trajectory prediction, transient instability detection and transient emergency control. Moreover, potential deficiencies and solutions are also discussed based on the analysis.