Abstract: To study the influence of demagnetic field in the hydrostatic high pressure vessel, we selected 6 samples with different slice-number (n=1, 3, 5, 7, 10, 13) of amorphous alloy Fe46.3Co0.03Ni46.5Si3.75V0.92B2.5 ribbon, inserted them into multiple electric solenoid and measured the magnetization, magnetic permeability and initial magnetization, respectively, at 400 Hz. We found that: (1) The more the slices of sample, the stronger the influence of demagnetic field was, which leaded in surprising errors of m and i. For the sample with 1 slice, we obtained the optimal values, m=4 430, i=3 396. (2) With the increase of slice number (n=1~13), we measured saturation magnetic induction Bs=0.837～0.762T, indicating the influence of demagnetic field on Bs was much small. (3) To reduce the error from demagnetic field, thinner sample could be used, for example thin film with 0.2 m thick. (4) To eliminate the error from demagnetic field, closed magnetic circuit must be adopted, such as ring rolled up by amorphous alloy ribbon.