NOVELTY - Method for preparing bio-organic fertilizer involves (a) treating straw using alkaline solution, (b) treating straw using acid solution, (c) neutralizing treated straw, (d) uniformly mixing treated straw, rapeseed cake, animal feces and biological broth and fermenting mixture, (e) spraying diluted biological broth on fermented mixture, and fermenting mixture, (f) stacking fermented material, adding earthworm to stacked material to obtain manure, and (g) mixing manure with rapeseed cake, fermenting mixture, drying fermented mixture, and granulating dried mixture.    USE - The method is useful for preparing bio-organic fertilizer (claimed).    ADVANTAGE - The method shortens production time of bio-organic fertilizer, and the prepared fertilizer enables to improve soil fertility, provide nutrients to crop, promote growth of crop and increase crop yield.    DETAILED DESCRIPTION - Method for preparing bio-organic fertilizer involves (a) slicing straw into 2-5 cm pieces, spraying alkaline solution of pH 10-11 on straw pieces, until straw is moistened, allowing straw to react with alkaline solution for 2-5 hours, washing treated straw using water and drying washed straw, (b) spraying acid solution of pH 3-4 on dried straw obtained in the step (a), until straw is moistened, allowing straw to react with acid solution for 1-3 hours, and drying treated straw, (c) adding dried straw obtained in the step (b) into water, adding 40-50% calcium hydroxide solution to water for adjusting pH 6.9-7.1, allowing straw to be in water for 5-10 minutes, draining water from straw and drying straw, (d) uniformly mixing straw obtained in the step (c), rapeseed cake, animal feces, and biological broth in a ratio of 100:20-30:20-40:1-3, piling mixture, and fermenting mixture for 5-7 days, (e) fermenting mixture at 56-60 degrees C, spraying 50-100 times diluted biological broth when temperature reaches 65 degrees C, and fermenting mixture for 8-15 days, (f) spreading fermented material obtained in the step (f) until reaches room temperature, stacking cooled fermented material to thickness of 20-30 cm, adding 0.5-30000/m2 earthworm to stacked material, maintaining for 3-7 days, separating earthworm from stacked material to obtain manure, and (g) mixing manure obtained in the step (f) with rapeseed cake in a ratio of 20:2-5, fermenting mixture for 5-8 days, drying fermented mixture, and granulating dried mixture.