The invention provides an alternating current channel transmission capacity optimization method and device in an alternating current/direct current hybrid power system. The method comprises the stepsthat double-machine equivalence is carried out on a transmission-side alternating current system according to the dynamic response curve of an alternating current/direct current hybrid power grid, soas to acquire a leading generator group and a hysteresis generator group; Thevenin equivalence is carried out on the alternating current/direct current hybrid power grid from the direct current side according to the leading generator group and the hysteresis generator group; and finally the operation mode of the alternating current/direct current hybrid power grid is adjusted according to the Thevenin equivalence result of the alternating current/direct current hybrid power grid; and the alternating current channel transmission capacity is optimized in the direct current hybrid power grid. According to the invention, the problem that an alternating current channel is impacted by the collapse of the transmission power of a direct current transmission system during a recovery process and thevoltage drop of a direct current conversion bus after the generator group oscillating aroused by certain faults in the transmission-side alternating current system is solved; and reference is provided for a power grid operator to arrange the operation mode of the alternating current/direct current hybrid power grid reasonably to ensure safe and stable operation of the alternating current/direct current hybrid power grid.