NOVELTY - Method for preparing biotic agent involves mixing Bacillus subtilis, photosynthetic bacteria, denitrifying bacteria and lactic acid, heating mixture, inoculating B.subtilis and stirring mixture and adding soybean oil to mixture to prevent bacterial contamination, inoculating photosynthetic bacteria and allowing to stand and obtaining dark red medium and precipitated bacterium, inoculating denitrifying bacteria and stirring mixture and airing, inoculating lactic acid and stirring.    USE - The method is useful for preparing biotic agent for degrading nitrogen and phosphorus (claimed).    ADVANTAGE - The biotic agent is used in sea, fresh water culture pond and seedling pool and environmentally-friendly.    DETAILED DESCRIPTION - Method for preparing biotic agent involves mixing Bacillus subtilis, photosynthetic bacteria, denitrifying bacteria and lactic acid in a ratio of 1:2:10:2, heating mixture at 85 degrees C for 5 minutes, inoculating 5% B.subtilis into 100 l inoculum seed tank, stirring mixture speed at 150 rotation/minute, temperature at 37 degrees C for 17 hours and airing for 1-2 minutes/3 hours, again stirring mixture speed at 150 rotation/minute, temperature at 37 degrees C for 20 hours and airing for 1.5 minutes/3 hours, adding soybean oil to mixture to prevent bacterial contamination, inoculating 10% photosynthetic bacteria into 5 l inoculum seed tank and allowing to stand under 2000 Lx, temperature at 28-30 degrees C for 5 days, and again allowing to stand under 2000 Lx, temperature at 28-30 degrees C for 5-10 days, obtaining dark red medium and precipitated bacterium, inoculating 5% denitrifying bacteria into 100 l inoculum seed tank, stirring mixture speed at 150 rotation/minute, temperature at 28 degrees C for 5 days and airing for 0.5 minutes/3 hours, again stirring mixture speed at 150 rotation/minute, temperature at 28 degrees C for 5 days and airing for 0.5 minutes/3 hours, inoculating 5% lactic acid into 100 l inoculum seed tank, stirring mixture speed at 100 rotation/minute, temperature at 40 degrees C for 48 hours and airing for 0.5 minutes/3 hours, again stirring mixture speed at 150 rotation/minute, temperature at 28 degrees C for 5 days and airing for 1 minute/3 hours.