Life Cycle Assessment(LCA) technology is an effective means in determining sewage treatment processes scientifically. This paper uses a sewage treatment process facility as the main line with the application of LCA technology. The Whole Life Cycle of the municipal wastewater treatment plants is divided into three stages：construction stage, operation stage, discarding and removing stage. This paper analyses the whole life cycle of the municipal wastewater treatment plants by the basic framework of LCA. Not only environmental load but also economic and technical factors are contained in the LCA mode. It is demonstrated by the concrete example of two municipal wastewater treatment plants, with evaluating the advantages and disadvantages of the two treatment processes accordingly. 