The invention provides an AC-DC conversion circuit. Three phases of instantaneous power are coupled and added through a coupling unit, so that fundamental frequency and double-frequency fluctuations on various phases of bridge arms are effectively counteracted. A high-capacity capacitor does not need to be installed on each converter unit for suppressing single-phase fluctuation power, so that the volume of the AC-DC conversion circuit is greatly reduced. If the AC-DC conversion circuit is applied to a power electronic transformer, the volume of the power electronic transformer can also be effectively reduced and the cost of the power electronic transformer is reduced.