Abstract: This article focuses on the Profinet I/O protocol, combined with the practical needs of automated production lines, completes a full-process study from protocol principle analysis to programme development implementation. By constructing a hardware architecture based on Siemens S7-1500 PLC and Profinet remote I/O modules, it designs programme logic encompassing device configuration, data interaction, and fault diagnosis, and completes function testing and performance optimization in a simulated production line scenario. The results show that this programme can achieve millisecond-level data transmission for production line equipment, reduce the fault rate to below 0.3%, and meet the operational requirements of high real-time performance and high reliability in automated production lines.