The invention discloses an AC (Alternate Current) complementation method for a multipower system. In the AC complementation method, a transformer with a plurality of input ports is used as a power node, wind power and photoelectricity are respectively switched in the input ports of the transformer, grid electricity is switched in other input ports of the transformer, and an output of the transformer is connected with a user or a local area network, so that multipower complementation and power integration are realized at a user side of the transformer, wherein the wind power and the photoelectricity are switched into the transformer in a controlled mode; the grid electricity is switched into the transformer in an uncontrolled mode; the wind power, the photoelectricity and the grid electricity in the multipower system have the same frequency and the same phase; voltage classes of power subsystems can be unequal; and the voltage classes of the power subsystems and a voltage class of the grid electricity can be unequal. The AC complementation method for the multipower system has the significances of locally utilizing wind energy, optical energy and wave energy most conveniently and rapidly and furthest, reducing the requirement of the grid electricity on power capacity and achieving the low-carbon energy-saving and green environmental-friendly effects.