In this paper, Cu-substituted NiZn ferrites with nominal compositions of (Ni0.3Zn0.7)1−xCuxFe2O4 (0 ≤ x ≤ 0.4) were prepared by solid-state reaction method. Then, the structural, element composition, valence distribution, surface morphology and magnetic properties of the samples were investigated systematically. As the concentration of composition (x) increases, the lattice constant gradually decreases. When x = 0.1, the μ′ are much higher than of the pure sample, and the power loss lower than that of the sample without Cu, which indicating a significant improvement as substituting in an appropriately extend. Thus, the high permeability and low power loss can be obtained by the small addition of Cu in NiZn ferrites, which improve the application range of the NiZn ferrites.