Abstract: The characteristics of Modbus protocol were introduced, and the protocol libraries of Mod- bus RTU master were analyzed.It made sure that Modbus RTU protocol was adopted in data transmission between S7-200 PLC and intelligent remote receiver used in coal mine, and realized intercommunication between equipment for excavation and remote device. The application indicated that Modbus communication took S7-200 PLC as master has reliability in data transmission and good effect.