This article This paper is the preliminary design of sewage treatment plants, mainly described the characteristics of oxidation ditch process and application. Described the characteristics of oxidation ditch nitrogen and phosphorus removal, mechanism, oxidation ditch impact factors and nitrogen and phosphorus removal in various forms of nitrogen and phosphorus removal Oxidation Ditch. Finally, the future direction of the oxidation ditch to buy both energy-saving effect of phosphorus and nitrogen removal is the best. Described the oxidation ditch technology and the typical oxidation ditch process of development and characteristics of the oxidation ditch technology is also discussed prospects for development. Combined with the actual requirements, based on screening and assessment by the end decided to use oxidation ditch as the main structure of this project. By detailed calculation, the conclusion that the design of the sewage treatment plant conditions.