The invention relates to an emergency power control method for a flexible direct current-containing alternating current and direct current parallel serial power transmission system. When the alternating current and direct current parallel serial power transmission system suffers from power out of limit of an alternating current line caused by the reasons of increasing load of a receiving end, removal of an alternating current power transmission line and the like, active power which needs to be additionally transmitted by the flexible direct current line is evaluated by means of introducing an active power transfer factor, and then the transmitting power of the flexible direct current line is further regulated automatically to further eliminate the problem of power out of limit of the alternating current line connected in parallel therewith. The emergency power control method is simple in control links, easy to realize in engineering and high in control stability.