The invention relates to a dedicated composite bacterial fertilizer for saline-alkali soil and a preparation method of the composite bacterial fertilizer, and belongs to the technical field of composite bacterial fertilizers. The composite bacterial fertilizer is prepared from the following raw materials in percentage by weight: 10-20% of a phosphate-solubilizing potassium-solubilizing composite bacterial inoculant, 40-60% of kitchen waste, and 30-40% of diatomite, wherein the phosphate-solubilizing potassium-solubilizing composite bacterial inoculant is prepared by the following steps: respectively culturing and centrifuging bacillus megatherium, bacillus thuringiensis, pseudomonas fluorescens, bacillus amyloliquefaciens, bacillus mucilaginosus and azotobacter chroococcum, performing freeze drying on the centrifuged bacteria, drying, and performing balanced mix on the dried bacteria; the kitchen waste is prepared by the following steps: sorting the kitchen waste, removing impurities, dehydrating and removing oil from the kitchen waste, then crushing the kitchen waste, adding the composite bacterial inoculant and a mixed enzyme preparation, and at last performing aerobiotic solid state fermentation. The composite bacterial fertilizer is prepared by recycling the wastes such as the kitchen waste and the waste diatomite, so that the saline-alkali soil can be improved fundamentally.