NOVELTY - Preparing organic seaweed fertilizer involves removing sand of the seaweed, airing or drying the seaweed at 50-70 degrees C; crushing the dried seaweed to obtain the seaweed powder, then mixing it with water, regulating the pH to 2-3, regulating, breaking the wall by ultrasonic waves, extracting the mixture for 40-60 minutes with the ultrasonic waves at the ultrasonic powder of 125-200 w to obtain leaching liquor; and filtering and centrifuging the leaching liquor, then decoloring the obtained liquor by activated carbon, concentrating the liquor and drying the solid.    USE - For preparing organic seaweed fertilizer (claimed).    ADVANTAGE - The method of organic seaweed fertilizer is extracted ultrasonically; has short extraction time and high yield; avoids degradable denaturation under long-time and high-temperature conditions; avoids damage of high temperature and high pressure to the active ingredients, and needs no heating; solves the environmental pollution problem; turns the waste into wealth; saves the production cost; and has large economic value and profound environmental significance.    DETAILED DESCRIPTION - Preparing organic seaweed fertilizer involves removing sand of the seaweed, airing or drying the seaweed at 50-70 degrees C, making the moisture content be less than 10% to obtain dried seaweed; crushing the dried seaweed to obtain the seaweed powder, then mixing the seaweed powder with water in a mass ratio of 1: (15-25), regulating the pH to 2-3, regulating at 45-50 degrees C, breaking the wall by ultrasonic waves for the wall-breaking time of 0-12 minutes and at an ultrasonic powder of 100-125 w, regulating the pH to 4-5 after breaking the wall, extracting the mixture for 40-60 minutes with the ultrasonic waves at the ultrasonic powder of 125-200 w to obtain leaching liquor; and filtering and centrifuging the leaching liquor, then decoloring the obtained liquor by activated carbon (5%), concentrating the liquor, controlling the concentrating temperature at 45-50 degrees C, concentrating the liquor until the solid content is in 20-50%, and drying the solid to obtain the organic seaweed fertilizer.