The invention discloses an organic-inorganic improvement fertilizer for saline-alkali soil and a preparation method thereof. The organic-inorganic improvement fertilizer is prepared from, 20-30 parts of bentonite, 20-30 parts of zeolite, 20-30 parts of flue gas desulfurization gypsum, 10-20 parts of dehydrated sludge, 20-30 parts of humic acid, 10-20 parts of coal ash, 20-30 parts of ardealite, 10-20 parts of peat, 10-20 parts of straw meal, 10-20 parts of animal waste, 2-8 parts of microbial inoculation bacteria and 2-5 parts of emulsified asphalt. The invention further provides a preparation method of the organic-inorganic improvement fertilizer for saline-alkali soil. According to the organic-inorganic improvement fertilizer, the physicochemical character of soil can be improved, soil permeability and moisture and fertilizer preservation can be improved, the soil ion exchange rate can be improved, the PH value can be buffered, the chemical fertilizer consumption can be reduced, the crop yield can be improved, the product quality can be improved, the soil improvement effect can be improved, and the soil improvement cycle can be shortened.