Abstract: This study simulated the influent characteristic of unsteady-state sinusoidal curve with amplitude of±25% and period of 12h, by adjusting initial DO concentration in aerobic zones at unsteady influent equilibrium position, to discuss the relationship between unsteady influent and pollutants removal, variation in step-feed process, and obtain the optimal DO control parameters in aerobic zones. The results were as follows:the optimal initial DO concentration is obtained at 2.0mg·L<sup<-1</sup<. Under this condition, the effluent of COD、ammonia nitrogen(NH<sub<4</sub<<sup<+</sup<-N)、total nitrogen(TN)、total phosphorus(TP) are 21.82, 0.59, 11.87 and 0.26mg·L<sup<-1</sup<, respectively. With the unsteady influent fluctuation, the effluent COD exhibit a variation of piecewise function, but the effluent NH<sub<4</sub<<sup<+</sup<-N, TN and TP show with sinusoidal function. From the engineering design point of modified four step-feed process, the variation factor of total handling capacity is 1.25, can be considered within the scope of safety factor.