Abstract: The structure and permeability-frequency spectra of（Fe_0.5Co_0.5）_73.5Nb₂V₁Si_13.5B₉Cu₁ alloys annealed at different temperatures was investigated.XRD analysis showed that with the annealing temperature increased,the lattice parameter of α-FeCo（Si） crystallites decreased because of the large Co solubility in the α-FeCo（Si） solid solution and the average grain size increased appreciably.Permeability-frequency spectra from 1 kHz to 10 MHz was studied by using an impedance analyzer for nanocrystalline（Fe_0.5Co_0.5）_73.5Nb₂V₁Si_13.5B₉Cu₁ alloys annealed at different temperatures.It was shown that relaxation frequency（f₀） could get to 10⁵~10⁶Hz,moreover the relaxation frequency（f₀） increased with the annealing temperature increased,but the product of initial permeability（μ_i） and relaxation frequency（f₀） kept a constant.The reasons were analyzed by the equation of domain wall motion and domain wall pinning mechanism.At the end,the way about how to improve the property of nanocrystalline alloys in high frequency was discussed.