Oil monitoring is an effective method for judging the health of equipment and providing early warning of hidden dangers of equipment failure.The basic principles of the latest types of online sensors for monitoring wear particles in lubricating oil were reviewed,including bulk magnetic adsorption sensors,microfluidic capacitive sensors,metal scanning sensors,double-layer planar coil sensors,ultrasonic sensors,and optical sensors,and the advantages and disadvantages of various sensing methods and the challenges facing future development were discussed.It was pointed out that the highthroughput,highsensitivity and integrated sensor which can distinguish between metal and nonmetal abrasive particles and collect image information of abrasive particles are the focus of future technological research,and the integrated,intelligent and wireless sensor is the direction of future research and development.