The experimental system was established to analyze the detecting ability of the designed novel online ultrasonic wear debris sensor.Simulated wear debris with different range of size was used to measure the ability of the sensor to detect debris size.It is revealed that the sensor can detect debris with size from 45 μm to 220 μm.The toplimit of the senso〖JP3〗r’s〖JP〗 size detecting ability is about 220 μm and the sensor may detect wear debris smaller than 45μm.Theoretical calculation and contrastive experiment with the SpectroLNF Q200 (Particle Shape Classifier and Particle Counter) were carried out on detecting wear debris concentration.It is shown that the sensor can analyze oils containing wear debris with concentration as high as 14 000 particles per milliliter.