Abstract: This paper introduced in details the domestic and international background and development process of online monitoring system application, discussed the technical characteristics of TRM type roller mill equipped with on-line monitoring system, and introduced the work principle of the on-line monitoring system in TRM type roller mill. Through the introduction of the application in the large roller mill of Guangxi Fang Cheng Gang Yuan Sheng Co. Ltd., the effect of online monitoring system in the actual operation was analyzed.