The invention belongs to the field of automatic control and discloses an automatic three-way module circuit. The automatic three-way module circuit comprises a meter-reading signal detection circuit and a relay control circuit, wherein the meter-reading signal detection circuit is used for detecting meter-reading signal voltage and judging whether a power supply is loaded on a bus or not; the relay control circuit is electrically connected with the meter-reading signal detection circuit and is used for controlling a water meter reading path and realizing automatic switching control, remote data transmission and real-time rapid meter reading. The meter-reading signal detection circuit can be used for rectifying dropout voltage and outputting a direct-current level for driving an optical coupler and whether the power supply is loaded on the MBUS1 bus is judged through monitoring a CHK_MBUS1 level at the other end of the optical coupler; a selective switching-on/off function of the control circuit is determined by the power supply. The switching-on/off of an MBUS circuit, an MB1 circuit and an MB2 circuit can be controlled through whether a power supply end has voltage or not, so that the water meter reading path is controlled. The automatic three-way module circuit has the advantages of practicability and convenience, simplicity in operation, scientific and reasonable design, convenience for installation and relatively low cost.