NOVELTY - Preparation of fermented liquid seaweed fertilizer includes rinsing seaweed with water, drying, cutting, soaking in calcium hydroxide solution, performing desalination color shield treatment, drying, milling, and sieving; adding water, adjusting pH, adding glucoamylase and nonstarch polysaccharide enzyme, and ultrasound-assisted enzymatically reacting; adding glucose, yeast extract, potassium dihydrogen phosphate, magnesium sulfate heptahydrate and calcium chloride, and adjusting pH; adding into liquid fermentation tank, inoculating, and aerobically fermenting.    USE - Method for preparation of fermented liquid seaweed fertilizer (claimed).    ADVANTAGE - The method produces large amounts of soil bacteria and variety of specific metabolites, enhances biological activity of seaweed fertilizer, fully retains seaweed rich nutrients, avoids alkali process and high temperature and pressure damages, and it has increased acid hydrolysis and pure microbial fermentation of more than 30%. The fertilizer has 40-60 g/L alginic acid content, effective viable count of greater than or equal to 2000000000/mL, natural nutrients and antibiotic substance contents, and organic, microbial and micronutrient fertilizer composite effect.    DETAILED DESCRIPTION - Preparation of fermented liquid seaweed fertilizer comprises (A) rinsing seaweed with water to remove impurities, drying, cutting into 3-5 cm length, soaking in 0.1 wt.% calcium hydroxide solution having pH of 6.5-7 for 3 times every 15 minutes, performing desalination color shield treatment, drying to 85 degrees C, milling, and sieving through 40 mesh sieve; (B) adding 8-10 times water, adjusting pH to 6.8-7.2, adding 2-3 wt.% glucoamylase and 1-2 wt.% nonstarch polysaccharide enzyme, and ultrasound-assisted enzymatically reacting to 40-60 degrees C for 2-4 hours at ultrasonic power of 400 W and frequency 25 kHz; (C) adding 3-5 wt.% glucose, 2-3 wt.% yeast extract, 0.3-0.5 wt.% potassium dihydrogen phosphate, 0.02 wt.% magnesium sulfate heptahydrate and 0.01 wt.% calcium chloride, and adjusting pH to 7-7.2; (D) adding into liquid fermentation tank, inoculating with 2-3 wt.% Bacillus subtilis, 2-3 wt.% Bacillus megaterium, and 1-2 wt.% Aspergillus niger, and aerobically fermenting to 28-37 degrees C for 8-12 hours while stirring at 150-300 revolutions/minute at flow rate of 10-20 L/minute; and (E) filtering supernatant for production of compound fertilizer while adding fermentation broth with 3-5 wt.% phosphorus, potassium and nitrogen-fixing bacteria strains, and 30-40 g/L copper, iron, zinc, manganese, boron and other trace element.