A cylindrical capacitive sensor was developed,which has the advantages of high resolution,small size and designability,and can be easily installed on lubricant pipeline to monitor the debris in lubricant of aircraft engine.A theoretical model of the cylindrical capacitive sensor was set up to analyze several parameters’ effectiveness on the performance of sensor,including the cross sectional area of the sensor,the distance between two poles and the permittivity.It is shown that the capacitance value of the sensor is increased with the increase of the debris number,as well with the increase of debris size;there are approximately linear relations for above two cases.Numerical simulations were conducted to determine the optimal parameters for preliminary experiments.Experiments were carried out to demonstrate the feasibility of the developed capacitive sensors.