The invention relates to the field of fertilizer preparing, and discloses a bio-organic fertilizer and a preparing method thereof. The bio-organic fertilizer is prepared from 180-220 parts of chicken manure, 380-420 parts of sheep manure, 380-420 parts of furfural residues, 38-42 parts of calcium superphosphate, 4-6 parts of compound bacteria liquid, 8-12 parts of bran, 8-12 parts of a mixture of rice bran and hulls, 4-6 parts of growth promoting agent, 8-12 parts of oxygenation particles, 8-12 parts of insecticide and 8-12 parts of binding agent. The preparing method includes the steps that 1, the compound bacteria liquid, the bran and the mixture of rice bran and hulls are mixed, and a mixture is obtained after drying; 2, composting fermentation is carried out after the chicken manure, the sheep manure, the furfural residue and the mixture are mixed and stirred; 3, after fermentation materials are dried, smashed and screend, the fermentation materials and residual components are mixed, and finally a finished product is prepared after stirring, pelleting and drying. The bio-organic fertilizer is good in particle molding and high in fertilizer efficiency, and has the effects of killing pests and promoting plant growth.