Abstract: The nanocrystalline cores were subjected to secondary transverse magnetic field annealing at 420-460 ℃, and the applied magnetic field strength was 800 Gs. X-ray diffractometer was used to measure the crystal phase structure of the strip, precision magnetic component tester was used to measure the inductance L of the cores and soft magnetic AC equipment was used to measure the the magnetic loss P_s of the cores. The results show that the secondary transverse magnetic field annealing process can improve the high-frequency soft magnetic properties of nanocrystalline cores. When the frequency is 100 kHz, the effective magnetic permeability μ_e, coercivity H_c and magnetic loss P_s of the cores are 24.2 k, 1.20 A/m, 6.1 W/kg(B_m=0.1 T)respectively after only nitrogen annealing at 550 ℃.However, the effective permeability μ_e is increased to 31.5 k, the coercivity H_c is reduced to 0.96 A/m, and the magnetic loss P_s is reduced to 4.9 W/kg (B_m=0.1 T)after the second transverse magnetic field annealing at 440 ℃.