An online monitoring method for the main drive system of rolling mill is studied in this paper. The monitoring objects are drive shaft torque, rolling force, and other related process signals of the rough rolling mill. A non-contact torque measurement method based on induction power supply was adopted, and this kind of power supply for sensors and transmitters can provide a long-term stable power supply, and make the system work continuously. The overall monitoring system includes signal acquisition module, network communication module, database server module, status monitoring and alarm module, signal processing and analysis module, and client server module. The realization of the monitoring system can help to prevent catastrophic damage and reduce additional costs due to unexpected downtime.