This article briefly introduces the development and application of urban sewage treatment based on data feedback system, and introduces the background of cloud computing and the development history of composite ecological treatment technology for sewage treatment. By constructing a bacteria-algae-floating bed composite system, based on the study of its effect on water purification, its mechanism characteristics were discussed. Construct a bacteria-algae-floating-bed composite system to purify sewage with different concentrations, and explore the distribution characteristics of nitrogen cycle bacteria and the evolution process of phytoplankton community.