TECHNOLOGY FOCUS - AGRICULTURE - Preferred Method: The step (i) comprises removing sludge from fresh seaweed or other impurities. In the step (ii), the amount of water added to the fresh seaweed slurry is 0.3-1 times, preferably 0.65 times. In the step (iii), the amount of complex enzyme added to the seaweed slurry is 0.2-1%, preferably 0.6%. The complex enzyme is cellulase, pectinase and/or protease, preferably cellulase and/or protease. The amount of microbial fermentation inoculant added to the seaweed slurry is 0.4-0.7%, preferably 0.6%. The microbial fermentation inoculant comprises Bacillus subtilis and/or Bacillus licheniformis. In the step (iii) of thermal insulating, the temperature is maintained at 25-45 degrees C, preferably 30 degrees C. The fermentation time is 90-100 hours; and the pressure in the fermentation tank is controlled at 0.01-0.02 MPa. In the fermentation process, adding sterilized air for each 4 hours, where the sterilized air ventilation volume is 0.4-0.8 times the capacity of the tank. In the fermentation process, stirring is carried out once for every 2-3 hours. In the step (iv), the acid-producing agent comprises Lactobacillus and/or Acetobacter. The method comprises (i) removing seaweed sludge or other impurities, (ii) crushing and grinding, passing through a small-mesh sieve to crush the seaweed cell, filling into the fermentation tank using suction machine, and carrying out high temperature sterilization, (iii) adding 0.3-1 times of purified fresh water into the seaweed, (iv) adjusting the pH value to 6.8-8.8, adding protease and cellulase enzymes of 0.2-1% the total mass of seaweed, adding Bacillus subtilis and Bacillus licheniformis of 0.6% the total mass of seaweed, and adding various substances at a time interval of 1-3 hours, (v) stirring uniformly, heating and thermal insulating, where the temperature is controlled at 28-60 degrees C, and the pressure is controlled at 0.01-0.02 MPa, adding sterilized air for 4-6 hours, where the sterilized air ventilation volume is 0.4-0.8 times of the capacity of the tank, stirring once for every 3 hours, and fermenting for 90-100 hours, and (vi) filtering the fermented solution, and adding Lactobacillus and Acetobacter to obtain the fertilizer. ACTIVITY - Fertilizer.