Abstract: An FeNi magnetic powder (Fe-50wt%Ni) derived from gas atomization first underwent a phosphatizing process, then was coated with a sodium aluminosilicate sol. Eventually, the surface modified magnetic powder was shaped by pressing and heat treated in N2 atmosphere, yielding a metal composite magnetic core.The results showed that the surface modified FeNi magnetic powder was uniformly coated by an insulation layer composed of nano-sized sodium aluminosilicate particles. The density and effective magnetic permeability of the obtained metal composite magnetic core decreased with increasing the amount of added sodium aluminosilicate, and the power loss of the magnetic core remarkably decreased when a proper amount of sodium aluminosilicate was added. When the added sodium aluminosilicate accounted for 0.5wt%, the effective magnetic permeability of the composite magnetic powder core reached the maximum of 122.4, and its DC superposition characteristic was measured to be 49.3% in a DC magnetization field of 100 Oe, and the power loss to be 168.2 mW·cm-3 under a testing condition of 50 kHz and 100 mT. Compared with the one using silicone resin as the coating agent, the composite magnetic powder using sodium aluminosilicate showed higher magnetic permeability frequency stability and lower power loss.