The invention relates to a double loop AC transmitting system and a control method thereof. The system comprises a microcontroller circuit, a three-phase electric acquisition circuit, a communication interface circuit and a power circuit for supplying power for whole transmitter; the microcontroller circuit is communicated with an upper computer through the communication interface circuit, and the microcontroller circuit also acquires three-phase electrical parameters through the three-phase electric acquisition circuit; and the three-phase electric acquisition circuit comprises a strong and weak electricity isolation module for realizing strong and weak electricity isolation and a three-phase electric signal acquisition and measurement module for realizing three-phase electric signal acquisition and calculation. According to the invention, two three-phase circuit can be monitored; the method can monitor multiple parameters; an RS485 upward communication interface is also provided, and remote maintenance is supported.