Abstract: Carbon emissions from municipal sewers are an important part of the total carbon emission verification and evaluation work in China′s sewage system, and also a blind spot problem that is faced at present. Clarifying its production and emission mechanism and occurrence scale, especially exploring the role of internal factors in the mechanism process, is a key prerequisite for achieving accurate evaluation. Focusing on the process of CO₂ production and emission mechanism, in order to quantify the effects of different hydraulic conditions and sewer sediment, gas chromatography and three-dimensional fluorescence spectroscopy were used to analyze the differences in CO₂ production and emission fluxes and degradation mechanism and influencing factors of dissolved organic matter (DOM) in sanitary sewer sediment (S_sanitary), storm sewer sediments (S_storm) and illicit discharged storm sewer sediments (S_mixed) under simulated high water level (C_A), no water (C_B) and intermittent high water level (C_C) conditions. The research results indicate that: (1) S_mixed has the highest cumulative CO₂ emission flux within 60 days under three working conditions, which are 2.36×10⁵, 1.95×10⁵, 2.03×10⁵ mg/(m²·d). (2) Among three conditions, the CO₂ production and emission of three types of sediments in C_B are most significantly inhibited, and the minimum peak daily CO₂ emission fluxes are all in C_B, which are 3.20×10³ mg/(m²·d)(S_sanitary), 3.60×10³ mg/(m²·d)(S_storm), 4.35×10³ mg/(m²·d)(S_mixed), respectively, indicating that exogenous carbon is the necessary condition for the stable production and emission of carbon dioxide in sediments. (3) In the early stage of sediment cycle culture, when overlying water was present, the tryptophan (λ_Ex/λ_Em=275 nm/340 nm) in DOM was significantly degraded in C_A and C_C, which was the main contributor to CO₂ production and emission in drainage channels. This study provides data support for the construction of a refined sewer carbon emission accounting and evaluation system and helps systematic carbon emission reduction programs. Future work needs to further elucidate the key role of the microbiome, especially the functional flora, in the pipeline carbon emission mechanism.