Abstract: In order to explain the specific impact of different hydraulic and water quality conditions on the diversity of microbial phylum and genus in the municipal drainage network sediment, this paper uses the microbial 16S rRNA gene sequencing technology to explore the Alpha and Beta diversity of the sediment microbiome, the sample groups, differences and their statistical relationships with different environmental factors and possible causes. The results show that: (1) The dominant bacteria in the bottom silt, Bacteroidetes, Chloroflexi, Firmicutes, Acinetobacter, etc., are all organic matter-degrading bacteria. As the concentration of exogenous carbon increases, the abundance of the same bacteria is higher. The more types of acidic organic matter, higher the diversity of bacterial communities. (2) Within a certain range, the higher the shear force, the higher the abundance of anaerobic bacteria (mainly used to decompose proteins and carbohydrates) such as Dechlomona (5.5%), Norrank_f_Anaerolineaceae (2.3%) and Longilinea (2.8%) with significant difference (P≤0.001) in sediment. (3) Within a certain range, the higher the temperature, the higher the abundance of the sediment microbiome. At 41℃, the relative abundance of dominant phylum Chloroflexi (11.1%), dominant phylum Defluviicoccus (4.9%) and Candidatus_Competitor (3.8%) with significant difference (P≤0.001) is the highest, while Proteobacteria, Bacteroidetes and other phylum may be affected by temperature due to microbial protein activity. (4) In an alkaline environment, only Proteobacteria (49.4%), Chloroflexi (10.1%) and other rod-shaped bacteria have the highest abundance and no filamentous bacteria. (5) SO₄²⁻ concentration has little effect on sediment microorganisms, but higher SO₄²⁻ concentration increases the abundance of Methylocystis, Zavarzinia and other microorganisms in the overlying water. It inhibits the growth of anaerobic microorganisms such as Methylocystis. The research shows that the diversity of microbiome in the sediments of gravity flow drainage pipes is related to five environmental factors: hydraulic shear, temperature, pH, SO₄²⁻ and exogenous carbon.