Abstract: An on-line detector for content of magnetic material in iron ore slurry was designed by use of solenoid inductance coil as detecting probe.The composition,working principle and software design of the detector were introduced.The detector can real-timely monitor change of content of magnetic material in iron ore slurry and improve efficiency of mineral separation,which also has characteristics of high anti-interference and accuracy and is easy to integrate other equipments because of using digital circuit.The test result showed that the detector can provide data at 0.5% accuracy.