TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preparation (claimed): Exopolysaccharide metabolite of aerobic Rothia sp. ZHT4-13 culture liquid is prepared by (A) preparing liquid fermentation medium comprising (g) sucrose (15-25), ammonium sulfate ((NH4)2SO4) (0.3-1.0), sodium chloride (NaCl) (2-8), magnesium sulfate heptahydrate (MgSO4.7H2O) (0.5-1.5), potassium dihydrogen phosphate (KH2PO4) (2-8), K2HPO4 (0.5-3.5), and distilled water (1000 ml); adjusting pH to 7.0-8.0; sterilizing at 120 degrees C and 0.1 MPa for 20 minutes; and inoculating seed liquid; (B) preparing seed culture medium by making nutrient agar solid slant, inoculating strain ZHT4-13, culturing for 1-2 days in a culture box at 34-36 degrees C, adding bacterial-free water with the volume ratio of 1:1, and swirling for 2-6 minutes at 15-35 degrees C to suspend strain in water and form stain cell seed liquid; (C) enlarging fermenting culture by inoculating 0.1-0.4 mol of seed liquid/100 ml of fermentation liquid, at 30-35 degrees C, and culturing for 3-4 days by swirling at 100-200 revolutions/minute (rpm); (D) extracting by centrifuging fermented strain liquid at 8000 rpm; adding cold ethanol (2-5 times the volume of fermentation liquid) in upper layer of fermentation liquid; centrifuging for 10-25 minutes at 9000-12000 rpm; obtaining precipitate; and drying in vacuum to obtain exopolysaccharide crude product; and (E) refining by adding water (0.5-1 times the volume of sample) into sample, swirling to vibrate for 1-5 minutes at 1000-2000 rpm, adding cold ethanol, which is 2-5 times the volume of sample to precipitate, standing for 8-24 hours at 4 degrees C in fridge, centrifuging for 10-25 minutes at 9000-12000 rpm, drying in vacuum, and obtaining microorganism flocculating agent MBF4-13 refined product. Preferred Component: The exopolysaccharide metabolite of aerobic Rothia sp. strain ZHT4-13 culture liquid is prepared by ethanol settling method. Preferred Parameter: In the seed culture liquid, the growth original pH is 7.0-8.0 and the growth temperature is 34-36 degrees C.