NOVELTY - Preparing organic fertilizer comprises (i) drying fresh cow dung, inoculating ferment bacteria, mixing, constructing stack fermentation, turning, and controlling compost fermentation temperature and time; (ii) preparing wormcast by feeding earthworms with composted cattle manure to obtain wormcast, stacking, subjecting composted cattle manure to windrow composting, and separating wormcast and earthworms; and (iii) mixing the composted cattle manure and wormcast in water, cooling, mixing cattle manure, wormcast and brown coal to obtain mixed organic material, and mixing with mixed fertilizer.    USE - The organic fertilizer is useful for reducing the empty rate of Chinese chestnuts (claimed).    ADVANTAGE - The fertilizer: is capable of obviously reducing the empty rate of Chinese chestnuts and the spider mite infection rate of chestnut trees; and promotes the root development of chestnut trees; solves the problem of unscientific fertilization of Chinese chestnuts; solves the problems that unscientifically treated poultry excrement, which is capable of polluting the environment, and nutrient source wastage; enables the empty rate of Chinese chestnuts to be reduced by more than 60% and the yield of Chinese chestnuts to be increased by more than 30%; and can achieve the remarkable synergism.    DETAILED DESCRIPTION - Preparing organic fertilizer comprises (i) cleaning fresh cow dung, and drying until water content is 65-75%, inoculating 0.1-0.7% ferment bacteria according to the weight of the fresh mixed material, uniformly mixing a layer of cow dung and a layer of dairy manure powder, constructing stack fermentation, when the hypha starts stacking and turning, controlling stack central temperature to not greater than 65 degrees C, turning once for 2-3 days during summer, turning once for 4-10 days during Spring and Autumn Period, and controlling compost fermentation temperature and time in 10-45 days; (ii) preparing wormcast by feeding earthworms with composted cattle manure to obtain wormcast, stacking or pruning, avoiding direct sunlight, subjecting composted cattle manure to windrow composting by piling, where the stack length is 100 cm, inoculating 0.1-0.5 kg earthworms, controlling stack temperature at 5-30 degrees C for 30-45 days, making cow dung into small grains, where color changed from brown to black brown, and separating wormcast and earthworms; and (iii) mixing the composted cattle manure and wormcast in water, respectively cooling to 25-35%, mixing the composted cattle manure, wormcast and brown coal according to mass ratio of (0.8-1.2):(0.8-1.2):(0.3 to 0.6) to obtain a mixed organic material, mixing the organic material with nitrogen-phosphorus potassium (NPK) boron-zinc mixed fertilizer according to mass ratio of (8-9.5):(0.5-1.5), where 1 ton of finished product organic fertilizer contains 10-20 kg urea, 10-20 kg diammonium phosphate, 10-20 kg potassium sulfate, 5-10 kg zinc sulfate, and 2-6 kg borax.