Abstract: The effects of powder preparation method, powder size and the addition amount of insulation agent on the performance of Fe78Si9B13 amorphous powder core were investigated. The results showed that the powders prepared by jet milling have fewer edges than those prepared by mechanical method. Most of the powders are roundel, which is more beneficial to insulation coating, so the properties are better. The powder grain size is greater, the magnetic powder core permeability is bigger, but the loss is bigger. As a result grain level deployment is needed. The best ratio is determined to be 70% of 75~100 μm powders, 10% of 61~75 μm powders, and 20% of 45~61 μm powders. The addition of insulation agent can improve the inherent resistance and reduce powder eddy loss, but too much insulation agent content will reduce the permeability. The optimal addition amount is 4% in this experiment.