The invention relates to the technical field of iron-rich phase modification. An iron-rich phase modifier comprises the following components by mass: 4.5-7.0% of Si, 2.5-5.0% of Fe, 0.7-1.4% of Mn, 0.03-0.1% of B, 0-0.15% of impurity elements and the balance of Al, wherein a preparation method of the iron-rich phase modifier comprises the following steps: placing Al, Al-Si, Al-Fe and Al-Mn in a melting furnace at a proportion for melting, then adding an Al-B intermediate alloy, and pouring the melt to form round ingots after degassing, impurity removal, heat preservation and standing, and slagging; the ingots are thermally extruded and processed to prepare an alloy rod after turning, sectioning and homogenizing treatment; and a modification method comprises the following steps: melting aniron-containing aluminum alloy, then adding the modifier, stirring, and then refining, standing, slagging and pouring to form ingots or performing production. According to the invention, a modification process is simplified, the impurity elements are reduced, and the dosage of the modifier is reduced.