Abstract: The Fe‒50%Ni magnetic powders (FeNi, mass fraction) derived from gas atomization first underwent the phosphatizing process, then were coated with the sodium aluminosilicate sol. Eventually, the metal composite magnetic cores were prepared through compacting process and nitrogen heat treatment by using the surface modified magnetic powders. The effect of coating agents on the properties of FeNi composite magnetic cores was studied. The results show that a uniform insulating coating layer of sodium silicaluminate nanoparticles is formed on the surface of FeNi magnetic powders, and the density and effective permeability of the composite magnetic powder cores decrease gradually with the increase of sodium silicaluminate addition. Proper addition of sodium silicaluminate can significantly reduce the power loss of magnetic cores. When the mass fraction of sodium silicaluinate is 0.5%, the effective permeability of the composite magnetic cores reaches the maximum value (122.4), and the DC superposition characteristic is 49.3% under the 100 Oe DC magnetization field. The power loss is 168.2 mW·cm^‒3 under the test conditions of 50 kHz and 100 mT. Compared with the silicone coating agent, the composite magnetic cores coated with sodium aluminate silicate gel show the better permeability frequency stability, and the power loss is reduced.