Abstract: The research on co-benefits is a new and very important area in the field of climate change policy research.The West-East Natural Gas Pipeline Project mainly aims at supplying abundant natural gas to Middle and East China,but it can also reduce air pollution and improve air quality in East China.Through applying a comprehensive environmental and economic simulation model for China,namely the Asian Pacific Integrated Model(AIM-Local/China),the authors conducted a quantitative analysis of the environmental co-benefits of the WestEast Natural Gas Pipeline Project by comparing the business as usual(BAU) scenario and the natural gas(NGS) scenario of the emission of SO₂ and CO₂ of the projects using the natural gas from this project.The result of the analysis shows that both the amount and extent of emission reduction of SO₂ and CO₂ are large.During 2003 to 2020,the emission reduction of SO₂ and CO₂ will be 3.12 million tons and 34.75 million tons respectively,and 40.5% and 17.9% lower than the BAU scenario respectively.Among the four sectors using the natural gas,the emission reduction of the electricity sector is the largest regarding both SO₂ and CO₂.