The invention discloses a WAMS-based ultra-low-frequency oscillation monitoring and emergency control method therefor. A WAMS-based ultra-low-frequency oscillation online monitoring method and a modelfor judging whether ultra-low-frequency oscillation occurs or not are given; by performing online judgment on whether a hydroelectric generating set provides negative damping or not, a speed regulator is further controlled in a targeted manner; and by combination with switching of speed regulator networking/isolated network mode, ultra-low-frequency oscillation can be quite down while certain primary frequency modulation capacity is maintained, so that a practical emergency control measure is provided for ultra-low-frequency oscillation control by a power grid dispatching operation staff, andtherefore, the control method is of significant practical meaning to power grid dispatching operation.