The invention discloses a method for preparing organic fertilizer from paper-making sludge. The materials such as paper-making sludge, amendment are mixed, subjected to high-temperature aerobic fermentation, post maturation and crushing, screened, and mixed with fertilizer of nitrogen, phosphorus, potassium and the like and medium and micro elements to prepare the organic fertilizer. The method has the advantages of simple process, easy operation, obvious innocuous effect, no environmental pollution and little nutrient loss; and the organic fertilizer prepared by the method is widely applied to industrial crops such as vegetables, fruit trees, Chinese herbal medicines, flowers and field crops such as wheat, corn, paddy rice.