The invention provides an organic fertilizer with livestock and poultry manure and a preparation method thereof. The organic fertilizer comprises cow manure, edible mushroom dregs, pig manure, chicken manure, maize straw powder and an Em (effective microorganisms) stock solution. The specific formula of the organic fertilizer comprises 19.7 percent of edible mushroom dregs, 10 percent of pig manure, 10 percent of chicken manure, 20 percent of maize straw powder, 0.3 percent of Em stock solution, and the balance of cow manure. The preparation method of the organic fertilizer is characterized in that a production technology of the organic fertilizer with the livestock and poultry manure mainly adopts a shallow pool type fermentation technology, namely the cow manure, the pig manure, the chicken manure, the edible mushroom dregs, the maize straw powder and the Em stock solution are poured into a mixer in proportion and are evenly mixed and stirred, the evenly mixed and stirred materials are sent into a shallow layer pool type fermentation pool, and the organic fertilizer fermentation environment temperature is controlled to be above 15 DEG C. Firstly, various raw materials including the livestock and poultry manure, the edible mushroom dregs, the straw powder and a fermentation bactericide are mixed, and then the mixed materials are put into a mixing and stirring machine to be evenly stirred, are sent into the material fermentation pool to be fermented for 8 days and are discharged from the pool to enter a secondary aerobic fermentation procedure. The organic fertilizer has the advantages of low cost and high yield and can improve the quality of crops.