The influence of high-temperature oxidation on soft magnetic properties of Fe78Si9B13 amorphous alloy was investigated using various analysis methods. The results reveal that a 10 mm thick iron oxide layer with high resistivity can be obtained on the surface of Fe78Si9B13 amorphous ribbons by high temperature oxidation treatment. It is found that the amorphous alloy magnetization becomes harder and the saturation induction density changes after the high-temperature oxidation. The saturation induction density value changes from Bs=1.42~1.46 T without chemical oxidation, to Bs=1.29~1.38 T after high-temperature oxidation. The factors which have a great effect on the magnetization difficulties of the amorphous ribbons were discussed