Abstract: This paper details the on-line monitoring system of BLA-FJ1 mine main fan with MCGS configuration software and Siemens S7-300 PLC as the core.The paper analyzes the structure composition and operating principle of this system,and discusses the design methods of monitoring software.the long-distance monitoring and parameter setting and other functions of mine main fan are achieved,using the advantages of industrial automation PLC’s high reliability and MCGS configuration software’s powerful man-machine interaction function.