The invention discloses a biological organic fertilizer which is composed of the following raw materials in parts by weight: 20-25 parts of chicken manure, 10-15 parts of cattle manure, 10-15 parts of sheep manure, 12-15 parts of peat soil, 6-10 parts of animal bone meal, 4-6 parts of animal wool meal, 4-6 parts of leaves, 6-8 parts of mushroom dregs, 0.01-0.03 part of copper oxide, 0.01-0.03 part of iron oxide, 0.01-0.03 part of magnesium, 2-4 parts of humic acid, 0.01-0.03 part of rhizobia, 0.03-0.06 part of azotobacteria, 0.01-0.03 part of phosphobacteria, 0.01-0.03 part of potassium bacteria, 2-4 parts of straws, 1-3 parts of egg-shell meal, 1-2 parts of rice chaff, 0.5-0.8 part of glucose and 0.05-0.08 part of borax. The invention also discloses a preparation method of the biological organic fertilizer. The biological organic fertilizer has high fertilizing capability, improves loose soil and protects ecological balance.