NOVELTY - Method for preparing organic fertilizer involves (a) weighing broken watermelon vine, adding e.g. hyacinth, then using humic acid and processing, (b) adding calcium hydroxide solution to processed mixture, and adjusting pH, (c) adding e.g. animal manure, mixing, stacking and fermenting mixture, (d) dispersing processed material, stacking material in greenhouse, putting earthworm, spraying soybean slurry, and culturing, (e) separating earthworm to obtain earthworm manure, and (f) adding e.g. rapeseed meal to earthworm manure, and fermenting mixture.    USE - The method is useful for preparing organic fertilizer for watermelon (claimed).    ADVANTAGE - The prepared organic fertilizer is rich in nutrients, easy to store, and easily absorbable by plants, and soluble in soil, promotes soil aggregate structure, soil permeability, water retention activity, and soil fertility, has easy contact with air, high utilization rate, quality, and organic matter content which is easily digested by earthworms, and increases surface area by more than 100 times compared to the surface area of organic matter which is not digested.    DETAILED DESCRIPTION - Method for preparing organic fertilizer involves (a) weighing 80-100 parts broken watermelon vine, adding 30-50 parts hyacinth and 5-10 parts shell powder, then using 5-20 parts humic acid and processing for 2-4 days, (b) adding 10-30% calcium hydroxide solution to the processed mixture obtained in step (a), and adjusting pH to 6.5-7.5, (c) adding 40-50 parts animal manure to the processed mixture obtained in step (b), and 1-3 parts microbial block, uniformly mixing, stacking and fermenting the mixture under closed condition for 15-20 days, (d) dispersing the processed material obtained in step (a) at room temperature, stacking the material in greenhouse to 20-30 cm thickness, and 1-2 m width, putting earthworm at night to 0.5- 30000/m2 at 20-26 degrees C, spraying soybean slurry every day to obtain moist material, and culturing for 10-15 days, (e) separating earthworm to obtain earthworm manure, and (f) adding 2-5 parts crushed Blumea balsamifera and 5-20 parts rapeseed meal to earthworm manure, and fermenting the mixture under closed condition for 10-20 days.