The invention discloses a method for processing alternating current system failures in an alternating current and direct current electric transmission line. The method comprises the steps of obtaining actual operation data of a power grid; according to overload capacity designed for direct currents, confirming power value, capable of being instantly increased or reduced, of a direct current system, and designing the transmission function controlled by direct current emergency power; obtaining the generator tripping value needed when the direct current emergency power is adopted to control conditions under failures of an alternating current system through an offline computing mode, pushing out action effect of the direct current emergency power control on the alternating current system failures, and making an offline control strategy; when the alternating current system failures occur, judging whether to adopt the direct current emergency power control according to the strategy, and safely and stably controlling the device to adopt generator tripping or load tripping measures according to the strategy. According to the method, the direct current emergency power control and the safe and stable control strategy are combined, a direct current emergency power control method is adopted to reduce total generator tripping value after the alternating current system failures occur, and overall economic benefits of power grid operation is improved.