The in fluences of magnetic field heat treatment and multiple tempering on the magnetic properties of an AlNthe magneticsteel horseshoe intended for a YF-65 servo valve are studied in this paper. After optimum magnetic field heat treatment and multipletempering, Br, Hc, (BH)max and the appliance gap magnetic flux density are 1350 mT, 62.1 kA/m, 54. 1 kJ/m3 and 225 mT~235mT, respectively.