The invention discloses an organic fertilizer for improving saline-alkali soil and a preparation method of the organic fertilizer. The organic fertilizer for improving the saline-alkali soil comprisesthe following ingredients in parts by weight: 30-38 parts of animal waste, 10-16 parts of plant straw, 8-12 parts of desulfurized gypsum, 6-10 parts of pulverized fuel ash, 5-7 parts of tea fluff, 4-6 parts of bagasse, 3-5 parts of waste tobacco material, 3-5 parts of seaweed meal, 2-4 parts of a pH regulator, 2-4 parts of mineral powder, and 1-3 parts of a deodorant and further comprises 1-3 parts by weight of a microbial agent and 0.01-0.03 part by weight of rooting powder. The organic fertilizer is prepared by granulating the animal waste, the plant straw, the desulfurized gypsum, the pulverized fuel ash, the tea fluff, the bagasse, the waste tobacco material, the seaweed meal, the pH regulator, the mineral powder, the deodorant, the microbial agent and the rooting powder. The organicfertilizer can effectively improve a soil structure of the saline-alkali soil and soil fertility, and reduce salinity and alkalinity; and when the organic fertilizer is matched with plant cultivation,the organic fertilizer further improves the water retaining capacity of the soil, avoids accumulation of salt in the surface soil, and can persistently and effectively improve the saline-alkali soiland change wasteland into fertile farmland after several cycles.