The magnetic properties of alumite magnetic film and its application are investigated. The alumite magnetic film is known to perpendicular magnetic media. The preparation process of alumite magnetic film is controlled to get the maximum energy product. This film was formed on the side of rotary drums, and multipolariy magnetized, then assembled with MR sensor to new precision magnetic t"otat"y encoders. And the properties of magnetic anisotropy, magnetic output dependance on recording wavelength 1 related to magnetised depth were discussed.