The invention belongs to the field of preparation of metallic soft magnetic materials, and particularly relates to a preparation method for a mu75 magnetic powder core of soft magnetic ferrosilicon aluminum, which includes steps of smelting, rough smashing, heat treatment, fine smashing, annealing treatment, powder grading, powder insulating, compression molding, secondary heat treatment and coating treatment and requires components, by weight, 9.10% of silicon, 5.95% of aluminum and the rest iron. The preparation is performed with the smelting temperature of 1600 DGE C, the compression molding pressure ranging from 1700MPa to 2000Mpa, magnetic powder core pressing temperature ranging from 600 DEG C to 800 DEG C, and one hour for warm keeping in a nitrogen-oxygen mixed atmosphere. The magnetic powder core mu=75+-6 at 100kHz, the magnetic conductivity mu is smaller than 1% in variation under 1000kHz, the magnetic powder core loss is accordant to Pcv (powder loss) 50kHZ/50mT<=100Mw/cm3, and the direct-current bias magnetic field is not lower than 70Oe when the magnetic conductivity is reduced to 50%. The preparation method for the mu75 magnetic powder core of soft magnetic ferrosilicon aluminum has the advantages that added binder is solid organic binder, the heat treatment after molding includes keeping warm for one hour in the nitrogen-oxygen mixed atmosphere, and the prepared magnetic powder core is free of pulverization, high in strength and stable in performance and has fine direct current bias characteristics, frequency stability and low loss.