Using coagulation sedimentation process in the advanced treatment of urban secondary effluent which can be recycled to circulating cooling water system in power plant is only perform well on turbidity removal. But the concentrations of organic matter and NH3 in effluent can not meet the requirements of circulating cooling water. Therefore, the feasibility of biological aerated filter (BAF) as a pretreatment enhancing coagulation sedimentation process was studied. The results show that the BAF pretreatment removes NH3 effectively, and the turbidity and CODCr of effluent of BAF-coagulation sedimentation process is much lower than individual coagulation sedimentation process. The final effluent qualities meet the requirements of circulating cooling water system in power plant.