The invention provides a method and a system for pre-warning and controlling the cascading failures of a large-scale alternating current and direct current hybrid power grid. The method comprises thefollowing steps: monitoring the status information of power grid equipment; when the power grid is in a failure-free operation condition, evaluating the interruption risk of the equipment based on themonitored status information; when the power grid is disturbed, identifying equipment status based on the monitored status information, and performing prevention and control measures set in advance according to the equipment failures; and when the power grid breaks down, carrying out cascading failure splitting control based on the monitored status information. Through the technical scheme provided by the invention, the blanks of cascading failure pre-warning and quick control based on wide-area network actual measurement information in the large-scale alternating current and direct current hybrid power grid are filled, and a cascading failure pre-warning, prevention and control and active splitting control method is provided for extra-high voltage alternating current and direct current hybrid power grids.