The invention provides a ferro-nickel alloy and a preparation method thereof. The ferro-nickel alloy is prepared from, by mass, 30% to 32% of Ni and 68% to 70% of Fe, and the average grain size of theferro-nickel alloy ranges from 10 nm to 18 nm. The ferro-nickel alloy is prepared through an electro-deposition method, the concentration of nickel salt in an electro-deposition solution is low, theferrite concentration is high, an additive is stable, and electrolyte can stably work for a long time. The Ni-Fe alloy is high in strength, low in linear expansion coefficient, high in ductility, small in average grain size and good in surface gloss. According to the ferro-nickel alloy and the preparation method thereof, a magnetic field is introduced in the electro-deposition process, increase ofgrains is restrained, the grains are refined, and the (002) faces of the grains are subjected to preferred orientation.