Model-based optimal control study of the six-tank integrative activated sludge process was carried out, and two step running time control strategies based on the cycle running feature of six-tank process were proposed, i.e. Fix_time strategy and NO3_control strategy. The step running time of the former was fixed, while that of the latter was controlled by SNO3 and its variation rate detected by the on-line sensors in the anoxic tanks. There were 7 parameters in Fix_time strategy and 6 parameters in NO3_control strategy needed to be determined. The two strategies were analyzed in multi-objective optimization method considering effluent quality and energy consumption simultaneously. The results showed that NO3_control strategy was more adaptive than Fix_time strategy because it could meet the time-demand of denitrification, and therefore, NO3_control strategy had better effluent quality with lower energy consumption. This research indicates that NO3_control strategy can improve the performance of the six-tank integrative activated sludge process.