Abstract: In view of the low biological denitrification efficiency of low-temperature sewage, the low-temperature sewage was treated by an organic polymer composite hard particle bio-carrier(OPCRP)-SBMBBR reactor. Compared with the traditional SBR reactor, two sets of reactors were analyzed by Miseq high-throughput sequencing technology. The difference in bacterial flora diversity and compositional abundance of activated sludge in the medium revealed the efficient treatment of the dominant nitrogen-depleting bacteria in low-temperature sewage. The results showed that under the condition of water temperature at (6.5±1) ℃, the effluent denitrification effect and sludge settling rates of OPCRP-SBMBBR reactor were obviously improved. Adding fillers could improve the diversity of nitrification and denitrifying bacteria in activated sludge system. And the relative abundance, the total abundance of dominant ammonia oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB) and anaerobic denitrifying bacteria increased from 3.9%, 3.47%, and 15.87% of SBR (R1) to 5.21%, 5.26%, 23.64% of (OPCRP)-SBMBBR (R2), respectively. Heterotrophic nitrification-aerobic denitrifying bacteria, including Rhodobacteraceae, Enterobacteriaceae, and Terrimonas increased from 2.77%, 1.63%, and 2.43% of R1 to 3.3%, 3.11%, and 2.5% of R2; and unique aerobic reaction nitrifying strains of R2, Pseudomonas, Hydrogenobacter, their relative abundances were 1.17% and 0.79%, respectively. The total relative abundance of dominant aerobic denitrifying strains in R1 and R2 were 10.66% and 17.35%, respectively; the total relative abundance of dominant nitrifying strains in R1 and R2 was 7.37% and 10.47%, respectively; the total relative abundance of dominant nitrifying and denitrifying strains in R1 and R2 was 28.65% and 43.32%, respectively, which provided a good bacterial environment for biological nitrogen removal in low temperature sewage.