Abstract: The (Co_0.94Fe_0.06)_72.5Si_12.5B₁₅ amorphous wire with different diameters was prepared by the the method of spin-in-rotating-water. After tension annealing, the magneto-impedance characteristic of the wire was measured. The results show that the wire has positive or negative GMI effect in different current frequency. Tension-annealing can improve the positive GMI effect evidently,and the less the diameter, the higher the sensitivity to the axial magnetic field. The maximum of the sensitivity is 124%/Oe.