Abstract: The experimental principles,contents and methods of an apparatus of law of magnetic circuit are introduced.The relationship between the series and parallel of magnetoresistance and magnetic flux Φ,and relative magnetic permeability of（non-） ferromagnetic material are conveniently measured by the magnetic flux Φ influence on input current of the apparatus.The characteristics of some magnetic materials are compared and analyzed.Also the parallel law of magnetoresistance and phenomenon of magnetic flux leakage are investigated,and a series of application experiments also offer teaching application.

Key words: magnetoresistance, relative magnetic flux ratio, relative magnetic permeability, law of magnetic circuit