A circuit is proposed for the multiple meter collection of State Grid.It through the feedback resistor to adjust the LDO to achieve control of M-bus bus level, save the bus current numerical dynamic use of capacitance, to receive and send data from the slaves. In this paper, the principle of the master circuit is described in detail, and the characteristics of the State Grid combined with the photoelectric isolation of the main control circuit. Practical application shows that the circuit has strong anti-interference ability, high reliability and high load capacity.