Abstract: Modbus protocol is the most widely used fieldbus for low voltage electrical applications. However, while following the message structure defined by Modbus protocol, manufacturers use different rules and implementations in product application. This paper studies the communication performance of Modbus RTU between representative brands of PLC and intelligent instruments, as well as introduces the realization method of remote monitoring and data sharing of underlying devices based on Modbus RTU communication protocol by developing experimental cases. The experiment shows that the master-slave monitoring system with low cost and high performance can be easily and reliably realized by following Modbus parameter settings and address correspondence rules between different brand devices and reasonable setting of polling rules for communication instructions of master and slave stations, which has certain reference and guiding significance.