An on-line monitoring system of hydrodynamic lubricant supply conditions for the back-up roll’s oil film bearing of 1420mm cold rolling mill was developed for providing real time monitoring so as to avoid unexpected breakdown of the production line. The monitoring parameters of supply pressure, supply temperature and supply flow rate show that the monitoring system software with real-time event trigger mechanism and intelligent storage algorithm solves the issue of data overflow in the continuous record and ensure the safety of data transmission. Test results for hydrodynamic lubricant supply conditions in the industrial production are reported, which indicated that established software architecture and programming methods construct a stable and reliable monitoring system, which provides early warnings for the safe production.