Wear condition of journal bearing was experimentally monitored with an On-Line Visual Ferrograph (OLVF) system. The round bearing was made of 45# steel with babbitt alloy bushing and the bearing journal was made of 45# steel. High stress of the water content of 0%,1%,3% in lubricant, 10 times of a normal load of 2200 N, and the rotating speeds at 500, 1000, 2000 rpm were adopted in accelerated experiment. A quantitative index of particle coverage area (IPCA) together with wear debris ferro-image was used to characterize wear degree and wear mechanisms. Three wear stages with corresponding wear debris ferro-images were identified from IPCA variations characterized by bathtub curve trend. The first one was running-in stage characterized by the highest wear debris producing rate and higher large debris content. The second one was normal wear stage characterized by the lowest wear debris producing rate and small normal debris. The final one was failure initiation stage characterized by higher wear debris producing rate and higher large debris content. The corresponding dominant wear mechanisms were micro-ploughing and micro–cutting induced by rough initial surfaces in the running-in stage, local rub due to vibration in the normal stage, and fatigue and abrasive wear in the failure initiation stage.