The invention provides iron-based amorphous alloy and a preparation method. The iron-based amorphous alloy comprises iron-based metal materials and additives, wherein the iron-based metal materials comprise pure iron, iron-phosphorus intermediate alloy and iron-boron intermediate alloy; the additives comprise boron oxide and soldering flux. SiO2 in the soldering flux reacts with Fe so that beneficial alloy elements can be supplemented into melt. B2O3 covers the surface of the melt to protect the melt, and then the burning loss of the element B and the element P is reduced. Therefore, the contents of the elements in the melt are kept balanced, and the amorphous forming capability and the soft magnetic performance are improved. The iron-based amorphous alloy prepared through the method has relatively high saturation magnetic induction intensity and relatively strong amorphous forming capability, and the saturation magnetic induction intensity can reach 1.7-1.75 T at most.