Principle: when a non-uniform permanent magnetic metal magnetic liner is mounted in a ball mill, using its own permanent magnetic liner, One side firmly adsorbed on the cylinder and the end cap, the other side tightly adsorbed with ball mill crushed and small ferromagnetic media, forming a protective layer adsorption. When the protective layer reaches a certain thickness, the liner with grinding media in movement and the material is no longer have a direct impact and abrasion, thereby reducing the wear rate of the liner, the period of use of liner greatly extended. The protective layer is always in dynamic equilibrium of worn and the added, played the role of magnetic liner permanent protection. Magnetic Lining life can reach several times of the normal manganese steel liner.