NOVELTY - Micropolluted water with low-nitrogen ratio is denitrified by pumping raw water to upflow reactor with sulfur/limestone/forest tree waste filler inoculated with anaerobic sludge in which hydraulic retention time is 8 hours, continuously introducing thiobacillus denitrificans medium for dynamic culture domestication of sludge for 10 days until operation stabilizes at greater than or equal to 80% nitrate removal rate, continuously domesticating by pumping raw water for 10 days until biomembrane regrows, and pumping raw water to allow microorganisms to use sulfur in filler to obtain a stable biomembrane.    USE - Denitrification of micropolluted water with low-nitrogen ratio (claimed).    ADVANTAGE - The denitrification method increases heterotrophic denitrifying bacteria, forms mixed nutrition type nitrogen removal system, shortens domestication time, and has good anti-interface ability, and nitrogen removal effect without generating secondary pollution.    DETAILED DESCRIPTION - Micropolluted water with low-nitrogen ratio is denitrified by pumping raw water to upflow reactor with sulfur/limestone/forest tree waste filler inoculated with anaerobic sludge in which volume ratio of filler is 1:0.2-0.5:0.5-2 and hydraulic retention time is 8 hours, continuously introducing thiobacillus denitrificans medium for dynamic culture domestication of sludge for 10 days until operation stabilizes at greater than or equal to 80% nitrate removal rate in which thiobacillus denitrificans medium is 0.5 g/L sodium thiosulfate pentahydrate (Na2S2O3.5H2O) , 0.2 g/L potassium nitrate, 0.2 g/L potassium dihydrogen phosphate, 0.1 g/L sodium bicarbonate, 0.05 magnesium chloride hexahydrate, 0.001 g/L ferric sulfate heptahydrate, and 0.05 g/L ammonium chloride, where Na2S2O3.5H2O is reduced to 50%, continuously domesticating by pumping raw water for 10 days until biomembrane regrows and Na2S2O3.5H2O is reduced to 0%, pumping raw water to allow microorganisms to use sulfur in filler for growth and propagation to obtain a stable biomembrane, where nitrate removal rate stabilizes at 80%, pumping raw water to flow reactor with stable biofilm, and discharing treated waste water.