In this paper, the simultaneous optimization of process structure and operation conditions for the coking wastewater biological treatment process is carried out based on a superstructure-based model. The superstructure proposed covers current widely used biological treatment processes in a coking wastewater treatment plant. The activated sludge model no. 3 calibrated for coking wastewater and thickening factors is chosen to describe the biological processes and the secondary clarifier, respectively. The optimization problem is formulated as a mixed integer nonlinear programming model (MINLP), which is implemented and solved using the general algebraic modeling system (GAMS). For given influent coking wastewater flow rate and composition as input, the O/A/O process and A/O/O process are selected for the influent with COD concentration of 2000 and 3000 g/m(3) respectively. The results provide the valuable information for the development and operation of activated sludge processes for coking wastewater biological treatment and useful insights for policy makers as well.