Several kinds of oil monitoring technologies were used for the state monitoring and fault diagnosis of gearbox in the SD22 style bulldozer including the oil chemical physics analysis,Ferrography analysis,Spectrometric analysis and so on.According to the monitored lubricating oil information and the shapes,sizes,quantities and styles of the abrasives in lubricating oil,the reasonable time to change new lubricating oil was determined.Based on the excessive levels of Fe and Cu elements in the oil,the conclusion is drawn that the friction plates or bearing cages exist serious wear and need to stop for checking.