The invention belongs to the field of metal materials, in particular to an aluminum-phosphorus-tin seed crystal alloy used for refining the primary silicon phase in a hypereutectic aluminum-silicon alloy and improving the wear resistance and processing property of the alloy and a preparation method of the aluminum-phosphorus-tin seed crystal alloy. The alloy is characterized by being prepared from, by mass, 83.5-98.9% of aluminum, 1.0-11.5% of phosphorus and 0.1-5.0% of tin, and in-situ synthesized micron or submicron grade aluminum phosphide seed crystals are distributed on an aluminum substrate. The preparation method comprises the following steps that raw materials comprising 75.0-95.0% of industrial pure aluminum and 5.0-25.0% of tin-phosphorus alloy 5are prepared; the industrial purealuminum is molten in a melting furnace and heated to 700-850 DEG C, and the tin-phosphorus alloy is added after temperature is stable; then, the temperature is gradually lowered to about 230 DEG C bymeans of a top-down directional solidification method, and an aluminum-phosphorus-tin seed crystal alloy ingot is obtained on the upper portion. The aluminum-phosphorus-tin seed crystal alloy prepared by the method has the controllable phosphorus content and low impurity element content; and the preparation method is environmentally friendly, saves energy, and is simple in equipment, good in controllability and suitable for industrial production.