A material composition for preparing an organic fertilizer from kitchen garbage is disclosed. The material composition comprises following raw materials by mass: 20-95% of kitchen garbage powder, 3.5-50% of straw powder, 1-30% of humic acid powder, and 0.5-1.5% of lactic acid bacteria powder, with the sum of the mass percentages of the raw materials being 100%. A preparing method of the organic fertilizer includes: subjecting recovered kitchen garbage to impurity removal, sorting, performing solid liquid separation to obtain solid state kitchen garbage with a low water content, smashing the solid state kitchen garbage, drying to obtain the kitchen garbage powder, adding the straw powder, the humic acid powder and the lactic acid bacteria powder into the kitchen garbage powder, and fully stirring. By the material composition and the method, the problems, namely a high cost for kitchen garbage treatment and transportation and liable pollution to the environment, are overcome, and the organic fertilizer manufactured can be absorbed by crops and prevents soil hardening caused by over fertilization, thus turning harm to good, turning waste materials into things of value, and achieving recycling and reutilization of the kitchen garbage.