NOVELTY - Preparing organic fertilizer involves: adding fresh oil slag, water and lipase into container, reacting at 30-45 degrees C for 40-50 hours to form lipase oil slag solution, boiling it, cooling, adding neutral protease, and then reacting at 50-60 degrees C for 2-3 hours and then spray drying to obtain protein hydrolysate; preparing phytase hydrolyzate and the plant ash extract; mixing uniformly protein hydrolysate, phytase hydrolyzate and plant ash extract to obtain organic fertilizer.    USE - For preparing organic fertilizer (claimed).    ADVANTAGE - The present method prepares organic fertilizer with good yield. The organic fertilizer obtained by the present method provides flexible nutrient proportion; increases crop yield; improves the crop quality; and is suitable for organic agricultural production.    DETAILED DESCRIPTION - Preparing organic fertilizer comprising 20-60 parts protein hydrolysates, 20-50 parts phytase hydrolyzate, and 20-50 parts ash extract involves: a) taking 200-500 parts oil slag, adding it into container, adding 1000-2000 parts water, adjusting the pH value to 7.5-8.2, then adding 0.5-1 parts lipase, stirring for 4-6 minutes, then reacting at 30-45 degrees C for 40-50 hours, stirring once every two hours for 2-4 minutes, to obtain the lipase oil slag solution, where the lipase is SUKAZYM-SUKALip lipase having enzyme activity 8000-16000 U/g; b) taking obtained lipase oil slag solution, boiling for 10-15 minutes, cooling, adjusting pH value to 7-8, then adding 0.01-0.05 parts of neutral protease, stirring for 3-5 minutes, and then reacting at 50-60 degrees C for 2-3 hours, stirring once every half hour for 1-2 minutes and then spray drying to obtain protein hydrolysates, where the neutral protease is SUKAPro NE neutral protease having enzyme activity of 30000-60000 U/g; c) taking 100-200 parts lipase oil slag solution obtained in step a), boiling for 10-15 minutes, cooling, adjusting pH value to 4.8-5.2, adding 0.02-0.04 parts phytase enzyme, stirring uniformly, then reacting at 55-60 degrees C for 2-3 hours, stirring once every half hour for 2-4 minutes, and then spray drying to obtain the phytase hydrolyzate, where the phytase enzyme is SUKAPhy phytase enzyme having enzyme activity of 3000-6000 U/g; d) taking 100-200 parts plant ash, adding 200-500 parts water, extracting for 20-30 minutes, stirring, filtering and then spray drying filtered liquid to obtain the plant ash extract; and e) mixing uniformly protein hydrolysates obtained in step b), phytase hydrolyzate obtained in step c) and plant ash extract obtained in step d) to obtain organic fertilizer.