This paper considered that putting the specialized soft magnetic material in the permanent magnetic field with a particular structure and the magnetic field strength can make it be magnetized, finally the surface of the soft magnetic material will produce twice strength than that of original permanent magnetic field. And we made a analysis for said phenomenon. We introduce d the deironing machines of permanent magnet strong magnet and high-gradient permanent magnet which are manufactured based on this principle. They can effectively remove the iron mineral of "kaolin" and its principles and structure is simple but it has the advantages of high efficiecy, energy saving, environmental protection. So it provides important references to chemical industry, ceramics and other industries which apply kaolin technologies.