The invention relates to the field of building materials, and particularly provides self-leveling dry-mixed mortar and a preparation method thereof. The self-leveling dry-mixed mortar comprises the following raw materials in parts by weight: 20-30 parts of ordinary Portland cement, 30-50 parts of steel slag, 1-10 parts of phosphogypsum, 1-5 parts of sepiolite powder, 0.1-2 parts of a high-efficiency water reducing agent, 0.1-1 part of a defoaming agent, 0.1-2 parts of carboxymethylcellulose ether, 1-10 parts of fly ash, 0.1-3 parts of basalt fiber and 0.1-3 parts of redispersible latex powder. The self-leveling dry-mixed mortar has the advantages of high strength, a smooth and flat surface after coagulation, good wear resistance, low cost and good environment friendliness.