The invention discloses a preparation method of an organic fertilizer, and relates to the technical field of organic fertilizers. The preparation method of the organic fertilizer comprises the following steps that 1, cow dung, chicken manure, pig manure, quicklime, pond mud, yellow bean pods, corn distillers' grains, compound zymophyte, corn straw powder, humic acid, bagasse, wheat bran, peanut cake powder, silkworm excrement, furnace slag, pitaya stems, banana peel, pineapple peel, grape pomace, passion fruit peel, bean curd, expired yogurt, durian peel, coffee residues, rice washing swill, earthworm manure, egg shells, bones, rotten vegetable leaves, shrimp shells, waste tea leaves, spoiled milk powder and trace elements are obtained by weight; 2, the cow dung, the chicken manure, the pig manure and the quicklime are mixed, dried and crushed to obtain excrement powder; 3, the excrement powder is mixed with the rest materials, and fermentation is conducted to obtain the organic fertilizer. According to the preparation method of the organic fertilizer, the fermentation process of the organic fertilizer can be accelerated, the fermentation time can be shortened, the fertility of theorganic fertilizer can be improved, and the disease resistance of plants is improved.