The invention relates to a saline-alkali soil fertilizer and a preparation method thereof. The saline-alkali soil fertilizer comprises decomposed coal, microorganisms, farmyard manure, straw, ardealite, ferrous sulfate, distillers' grains, a nitrogenous fertilizer, a phosphatic fertilizer and a potash fertilizer, wherein the microorganisms comprise nitrogen-fixing bacteria, phosphate solubilizing bacteria, potassium bacteria, fermentation bacteria and photosynthetic bacteria. The preparation method comprises the following steps: S1, mixing straw with farmyard manure, adding ferrous sulfate and the fermentation bacteria for fermentation; S2, adding ferrous sulfate, decomposed coal, microorganisms, ardealite and distillers' grains into the mixture in the S1, mixing and pelleting, so as to obtain fertilizer granules; 3, uniformly mixing and stirring the granules obtained in the S2 with the nitrogenous fertilizer, the phosphatic fertilizer and the potash fertilizer, so as to obtain the saline-alkali soil fertilizer. By adopting the fertilizer, the saline-alkali soil can be effectively reformed.