With increasing concerns about global warming, energy conservation and emission reduction have become a growing consensus and a global priority towards sustainability. As a fundamental infrastructure to sustain human activities and civil development, wastewater pipeline networks are receiving attention in the context of population growth and industrial expansion in urban areas. It is therefore quite challenging to analyze the environmental impact of wastewater pipeline projects and explore effective construction methods and strategies. A model to estimate CO2 emissions resulting from a typical wastewater pipeline project was developed based on life cycle theory. Wastewater pipeline construction emissions are divided into three categories: 1) material manufacture; 2) material transportation; and 3) pipe installation. The methodology for estimating CO2 emissions is demonstrated using a wastewater pipeline project in Suzhou, China. The results concluded that the materials consumed most by weight are sand, cement, cohesive brick, gravel, limestone, and UPVC pipe. It was also found that most of the emissions from material manufacturing were from UPVC pipe, which provide an insight into revealing the elements with significant reduction potential. CO2 emissions released by producing material accounted for approximately 87% of total emissions, while the emissions released in the other two categories were less than 13%. The unit CO2 emission of the studied wastewater pipeline construction project using traditional open-cut methods was 516.59 t CO2/km. This provides a reference for estimating CO2 emissions resulting from other wastewater pipeline projects.