The design scale of the Lanxi Wastewater Treatment Plant Phase II Extension Project is 60,000 m3/d. The main process is "regulating tank + pretreatment sedimentation tank + hydrolytic acidification tank + A/O bioreactor + secondary sedimentation tank + efficient sedimentation tank + ozone + aerated biological filter". The design effluent quality is carried out according to the first class A standard in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918—2002). Through the in-depth analysis of the existing problems in the operation of the Phase I Project, and in combination with the characteristics of the textile printing and dyeing wastewater in Lanxi Industrial Park, the process flow of this project is determined in a targeted manner. The process flow and the design parameters of the main structures are introduced and analyzed, which can provide the experience for the design of the similar projects.