Abstract: A radiation experiment with 8 MeV proton was carried out with an accelerator to study the magnetic property and the microstructure as well as the flaw distribution of the Fe-Ni soft magnetic alloy. It is shown that after the proton radiation, the coercivity of the Fe-Ni soft magnetic alloy goes up with the increase of the absorbed dose and the decrease of the magnetic permeability. The saturation magnetic induction remains stable. The XRD results show that irradiation does not cause phase changes in the structure, but causes lattice distortions. The positron annihilation analysis shows that the irradiation leads to vacancies and other flaws.