Municipal wastewater treatment plants (WWTP) are recognized as an important source of carbon emissions. Previous studies have calculated the CO2 emissions in the operating process of WWTP in the sight of engineering technology and the CO2 emission which is driven by the pulling effect of investment in WWTP are ignored. This paper calculates the CO2 emissions of wastewater treatment plant from the macroscopic view based on the input-output method and the fixed log-liner model. The study discovers that Compared to the indirect CO2 emissions from WWPT, the direct carbon dioxide emissions from WWPT are negligible.