NOVELTY - Preparing sodium alginate and organic fertilizer using gulfweed, comprises removing silt from the gulfweed, drying at 55-65 degrees C, crushing and soaking in fresh drinking water at 55-60 degrees C for 2-3 hours, regulating the pH to 4-6 using hydrochloric acid, adding 40% endo- beta -glucanase, 30% exo- beta -glucanase and 0.4-0.5% cellulase-containing 30% beta -glucosidase and carrying out enzymolysis for 8-10 hours, adding 45% neutral protease, 55% pectin lyase, 0.3-0.4% pectinase-containing 45% pectin esterase, continuing enzymolysis for 3-4 hours, stirring and carrying out centrifugal separation.    USE - The method is useful for preparing sodium alginate and organic fertilizer using gulfweed (claimed).    DETAILED DESCRIPTION - Preparing sodium alginate and organic fertilizer using gulfweed, comprises: (i) removing silt from the gulfweed, drying at 55-65 degrees C or taking dried gulfweed, crushing and soaking in 6-7 times volume of fresh drinking water at 55-60 degrees C for 2-3 hours; (ii) regulating the pH of the liquid to 4-6 using hydrochloric acid, adding 40% endo- beta -glucanase, 30% exo- beta -glucanase and 0.4-0.5% cellulase-containing 30% beta -glucosidase and carrying out enzymolysis for 8-10 hours; (iii) adding 45% neutral protease, 0.3-0.6% protease-containing 55% papain, 55% pectin lyase, 0.3-0.4% pectinase-containing 45% pectin esterase, continuing enzymolysis for 3-4 hours, stirring and carrying out centrifugal separation; (iv) adding the centrifuged gulfweed into 10-12 times amount of 2-4% sodium carbonate solution and digesting at 50-60 degrees C for 2-3 hours under a water bath; (v) diluting with 5-6 times volume of fresh drinking water at 50-60 degrees C for 1-2 hours, then filtering via 250-300 meshes tulle filter; (vi) adding 0.2-0.4% hydrogen peroxide solution into the filtrate and decolorizing at 50-60 degrees C for 1-2 hours, then raising temperature to 80-90 degrees C for 10-15 minutes, then filtering via 250-300 meshes tulle filter; (vii) slowly adding 3-4% calcium chloride solution (10%) into the filtrate, allowing it to stand for 1-2 hours, filtering, washing the impurities and residues in calcium alginate fibers with fresh drinking water; (viii) adding calcium alginate into 10-15 times amount of purified water, then adding 2-3 times of 10% sodium chloride solution, subjecting to ion-exchange in an water-bath at 50-60 degrees C for complete conversion of calcium alginate fibers into sodium alginate; (ix) precipitating with 95% alcohol to obtain sodium alginate, dehydrating the sodium alginate, drying and crushing into a product; and (x) dissolving 3-4 kg sugar in 25-35 kg water by stirring, then adding 0.6-0.8 kg sodium nitrophenolate and 0.5-0.7 kg sodium naphthalene acetic acid under stirring condition to dissolve completely and adding into the centrifugal filtrate of step (iii), crushing 23-25 kg fulvic acid into powder and mixing with 16-18 kg urea and 25-28 kg monopotassium phosphate solution, simultaneously adding 35-40 kg water and dissolving by stirring to obtain liquid fertilizer.