Sewage treatment is an efficient approach to achieving water resource recycling and safeguarding the environment. The municipal sewage treatment plants must not only meet discharge standards, but also incorporate energy-saving and carbon reduction measures during the sewage treatment process under China’s “dual carbon” strategy. This study calculated and analyzed carbon emissions from China’s municipal sewage treatment industry between 2012 and 2021, and forecasted the carbon emission intensity and amount in 2030. The findings revealed that the total carbon emissions increased from 29.33 Mt CO₂e to 58.95 Mt CO₂e over a decade, with direct and indirect emissions rising by 78.04% and 143%, respectively. Direct and indirect emissions in 2021 comprised 57.37% and 42.63% of the industry’s total carbon emissions, respectively. Sewage treatment plants accounted for the largest unit of carbon emissions, representing an average of 35%. Without effective carbon reduction measures, the industry’s carbon emissions are projected to reach 67.21 Mt CO₂e in 2030. Implementing two optimization schemes, the total carbon emissions in 2030 are anticipated to decline to 65.21 Mt CO₂e (Optimized 1) or 62.19 Mt CO₂e (Optimized 2), corresponding to a 2.98% or 7.46% reduction, respectively, showing a turning point of carbon peaking. These results can provide theoretical and data support for carbon neutralization planning in the sewage treatment industry, and are essential in achieving carbon reduction goals and addressing global warming.