Abstract: Ferrosilicon, ferrosilicon aluminum, and ferro-nickel magnetic powder cores were selected, and the effects of composition, particle size, and melting vacuum on the loss of magnetic cores were studied in this paper. The results show that, with the increase of Si content (mass fraction) in ferrosilicon magnetic powder cores, the core loss decreases gradually. When the magnetic powder core permeability is controlled at 60, the core loss is reduced to 380 mW·cm⁻³ under 50 kHz and 0.1 T test conditions, and to 140 mW·cm⁻³ under 20 kHz and 0.1 T test conditions, and the DC bias reaches 72%. For the ferro-nickel magnetic cores, the smaller the particle size, the lower the loss of ferro-nickel magnetic cores. The iron-nickel magnetic cores prepared by Fe–50%Ni powders in −400 mesh with the controlled magnetic core permeability of 60, the core loss is reduced to 120 mW·cm⁻³ under 50 kHz and 0.1 T test conditions, and to 320 mW·cm⁻³ under 100 kHz and 0.1 T test conditions, and the DC bias reaches 86%. For the ferrosilica-aluminum magnetic powder cores, the better the vacuum degree, the lower the loss of magnetic powder cores. Under the vacuum degree of 5 Pa, the permeability of the controlled magnetic powder cores is 60, the core loss is reduced to 65 mW·cm⁻³ under 50 kHz and 0.1 T test conditions, and to 180 mW·cm⁻³ under 100 kHz and 0.1 T test conditions, and the DC bias reaches 55%.