The project of boilertransforming from using coal into using natural gashas been launched in mainly city zonein Chongqing in order to cut down atmospheric pollution .The article points out that the transforming is the best choice of improving contaminative status in mainly city zonein Chongqing and brings forward the aim of the transforming. At the same time, by surveying and classifiying the scale and the range of the transforming, the authors analyze the technical and economical feasibilityof the transforming, primarilyanalyze and research environmental benefit that comes from the transforming. In the end, the article comes out the conclusion that implementation of the project not only brings definiteeconomical benefit, but also greatly cuts letting quantity of atmospheric contamination, which has effectively allayed atmospheric pollution in mainly city zonein Chongqing.