Abstract: The design and implementation of a system to decode and monitor the data of parallel communication between Siemens R30 computers are discussed. By decoding the communication protocols and line orders, with the designing hardware electrocircuits and software designed, a system is implemented to monitor the parallel communication between Siemens R30 computers and send messages to Siemens R30 computers from PCs based on Windows. The hardware electrocircuits are mainly composed of four parts for receiving, photoelectric isolation, CPLD control and single chip control electrocircuit. The software is composed of three modules, i.e., CPLD, single chip and microcomputer module where the alarm message interface (AMI) mechanism is applied to data distribution. This monitoring system has been put into on-line operation in a cold-rolling mill and proved stable and reliable and available to meet R&D needs.