The invention discloses a desulfurized gypsum preparation method based on saline farmland improvement. The preparation method comprises steps of flue gas collection, pulping, oxidation, heat treatment, condensation, dehydration, washing, and drying. The provided preparation method can reduce the water content of gypsum, increase the gypsum concentration, guarantee rapid crystallization, improve dehydration efficiency, save work time, and effectively improve the acid-base properties of soil.