In order to achieve the rapid, economical and efficient denitrification of actual low C/N wastewater, sodium thiosulfate and pyrite was used to treat the biochemical tail water for antibiotic production. The denitrification performance, the feasibility and stability of this practical wastewater treatment system were explored, and the microbial community was revealed by high-throughput sequencing. In this paper, three identical denitrification filter column reactors were used to fill 200, 400 and 400mL of pyrite with sodium thiosulfate dosage of 1、0.75、0.5times of the theoretical amount. The results showed that the removal rate of NO₃^--N in the first two reactors remained above 72%, while the denitrification performance of the third reactor was poor. The effluent pH value of the three reactors was basically between 6.8 and 8.0, which was suitable for the survival of sulfur autotrophic microorganisms without additional alkalinity. Compared with sulfur, sodium thiosulfate not only can be replenished at any time and avoid waste, but also can improve mass transfer between microorganism and electron donors, and slow down the blocking phenomenon of the system; The functional bacteria in the three reactors were Sulfurimonas and Thiobacillus, accounting for 27.32%, 25.37% and 18.4% respectively.