Abstract: The original wastewater treatment system in a tannery, whose process is "pre-aeration regulation tank→initial sedimentation→oxidation ditch→secondary sedimentation tank→Fenton treatment→ inclined pipe sedimentation tank", cannot meet the treatment requirements owing to the expansion of production scale and the improvement of wastewater discharge standards. Thus, the transformation project of the original wastewater treatment system was conducted, in which the treatment process of "adjusting sedimentation→pre-anoxic tank→A/O tank→second sedimentation tank→Fenton treatment→inclined pipe precipitation" was adopted. The concentrations of main pollutants in the effluent of the modified system can meet the standard requirements shown in Table 1 of "Discharge Standard of Water Pollutants in Huiji River Basin" (DB41/918-2014). Furthermore, the treatment cost was decreased and the pollutants were effectively reduced, which has good environmental and economic benefits.