NOVELTY - Organic fertilizer and preparation of the organic fertilizer are claimed. The organic fertilizer comprises fermented Eucalyptus leaf, cassava alcohol filter mud, shrimp and crab, and organic material-decomposing inoculum. The fermented Eucalyptus leaf is dried fermented Eucalyptus leaf. The shrimp and crab is dried shrimp and crab shell. The cassava alcohol filter mud is cassava effluent discharged during ethanol production. The organic material decomposition inoculum comprises specific commodity organic fertilizer producing-complex bacteria.    USE - The organic fertilizer is useful for preventing and controlling plant root knot nematodes (claimed) of various types, which are parasites on crops, preferably on the roots of melons, fruits and vegetables, to promote growth of plants.    ADVANTAGE - The organic fertilizer does not damage the conducting systems of plants to cause the problems that the plants on the ground are weak in growing, short and small, the color of leaves is abnormal, the fructification is few, the volume of production is low, and even worse, the plants can be damaged to die. The organic fertilizer overcomes defects in existing prevention and control methods that the killing process of root knot nematodes is incomplete, the price is high, the application is inconvenient, and the environment is vulnerable to be polluted. The organic fertilizer improves soil and quality of agricultural products, and can replace the existing pesticides for killing root knot nematodes. No chemical agent is added into the organic fertilizer, such that the organic fertilizer is suitable for the production of pollution-free food and organic agricultural products. The raw materials of the organic fertilizer are abundant, the production cost is low and the process is simple, thus the organic fertilizer is suitable for massive industrialized production.    DETAILED DESCRIPTION - Organic fertilizer comprises 30-60 pts. wt., preferably 40-50 pts. wt. fermented Eucalyptus leaf, 30-60 pts. wt., preferably 40-50 pts. wt. cassava alcohol filter mud, 3-30 pts. wt., preferably 5-20 pts. wt. shrimp and crab, and 0.1-0.2 pts. wt. organic material-decomposing inoculum. The fermented Eucalyptus leaf is dried fermented Eucalyptus leaf. The shrimp and crab is dried shrimp and crab shell. The cassava alcohol filter mud is cassava effluent discharged during ethanol production by pressure filtration, whose waste water content is 78-85%. The organic material decomposition inoculum comprises specific commodity organic fertilizer producing-complex bacteria, where the viable count of the bacteria is greater than or equal to 0.50 million/g with respect to performance standards NY609-2002. Preparation of the organic fertilizer, involves crushing fermented Eucalyptus leaf into pieces of 5 cm using crusher, drying the fermented Eucalyptus leaves, mixing fermented Eucalyptus leaf, cassava alcohol filter mud, shrimp and crab, and organic material-decomposing inoculum, adding the mixture into the base material, stirring the mixture uniformly, stacking and fermenting the mixture for 20-30 days at 60-65 degrees C and turning for 2-3 times at normal temperature, filtering the fermented product, drying till the moisture content is less than 30%, crushing and packing into granules.