Due to the wear particles in lubricating oil contain important information about the wear of engine components, wear particle monitoring is an effective method for judging the health status of engines and providing early fault warning. Online monitoring technology can provide real-time equipment status information. This article introduces the current online monitoring technologies for lubricating oil and abrasive particles, including capacitance method, resistance method，magnetic induction method, optical method, and acoustic method monitoring technologies. It discusses the monitoring principles, research results, advantages and disadvantages of each technology, analyzes the application status of the five monitoring technologies, and finally discusses the future development trend of lubricating oil and abrasive particle online monitoring technology.