The invention discloses a multipath alternating current split-phase synchronous sampling method and circuit. An A-phase alternating current quantity channel is gated by multipath analog switches and AD conversion is controlled to be started; after completion of conversion, a B-phase alternating current quantity channel is gated, and an A-phase conversion result is read to the internal RAM of an MCU processor; after time of T/(N*3), AD conversion is started, a C-phase phase alternating current quantity channel is gated after completion of conversion, and a B-phase conversion result is read to the internal RAM of the MCU processor; after time of T/(N*3), AD conversion is started, the A-phase alternating current quantity channel is gated after completion of conversion, and a C-phase conversion result is read to the internal RAM of the MCU processor so that sampling of one point is completed by three-phase alternating current quantity; and after time of T/(N*3), the steps are repeated to perform N sampling and then cyclic sampling of three-phase alternating current signals is completed. 2/3 of the A/D conversion channel is saved, utilization rate of the A/D conversion channel is enhanced, hardware resources are saved and hardware cost is reduced.