Combined with the background of international response to climate change, this study meets the needs of domestic ecological civilization construction and independent emission reduction. By defining the emission reduction mechanism of biogas projects, this study introduces the methane conversion factor and its application cases, and points out the importance of methane conversion factor and the limitations of the default methane conversion factor in the process of accounting carbon emission reduction, which laid the foundation for further exploration of the establishment of methane conversion factor calculation model for biogas fermentation.