Taking the typical friction pair cylinder liner-piston system of internal combustion engine as the research object,the condition monitoring test bench of cylinder liner-piston system of internal combustion engine was designed and built.Aiming at the shortcomings of the traditional maximum entropy method in analyzing the monitoring data of wear debris in oil,an improved fractional moment maximum entropy method (FM-MEM) was proposed,and the key parameters were optimized by combining the carnivorous plant algorithm (CPA).The threshold division of the monitoring data of wear debris in oil was carried out to evaluate the health status of the internal combustion engine.Combining theory with experiments,with online wear debris monitoring as the main focus,the running state of the cylinder liner-piston system of the internal combustion engine was monitored from three aspects,wear debris in oil,physical and chemical indexes,and surface morphology.The wear health status and the change trend of wear debris concentration in each time period of the cylinder liner-piston system under low speed condition were analyzed.Through the on-line wear debris monitoring test of the internal combustion engine,it is proved that this method can realize the on-line real-time condition monitoring of the cylinder liner-piston system of the internal combustion engine.