The detection of metal debris in oil is very important for monitoring the machinery. Based on the electromagnetic induction principle, a micro inductive sensor is designed and fabricated. This sensor is embedded in oil pipe as the oil circulates in the oil system. The micro-sensor can test more oil sample than other micro inductive sensor with micro pipe. An analog on-line detection system is built and the detection experiments are carried out in this paper. The oil samples with copper debris and iron debris are detected separately. The size of debris is between 88μm and 100μm. A simulation is carried out to analyze the trace of debris in oil with the software of Comsol. The accurate position of debris in oil pipe can be obtained according to the simulation result. The position and the size of debris relate to the inductance signal. With the accurate position of debris, the size of debris can be obtained according to the value of the inductance signal. The study designs an inductive sensor, and it can do high-through sample detection. The simulation gives a model to analyze the trace of metal debris in oil. The method has reference value for forecasting mechanical failure and monitoring the machinery. The simulation lays the foundation to study the distribution of metal debris. It is useful to study the relation between the size of debris and the inductance signal.