In order to further investigate activated sludge system for better carbon metabolism and nitrogen removal with less energy consumption, a new kinetic model was established. The detailed description of the proposed model was introduced for understanding the mechanisms involved in the activated sludge system, especially simultaneous substrate storage and biomass growth (SSSG) processes and soluble microbial product generation. The evaluation of the proposed model was demonstrated by a lab-scale sequencing batch reactor (SBR) operated with three different sets, i.e., aeration/non-aeration (set 1), non-aeration/aeration/non-aeration (set 2), and alternating aeration/non-aeration (set 3) processes. The purpose was to investigate carbon metabolism under multiple aerobic/anoxic conditions. The calibrated results showed quite an acceptable model fit to the on-line measured dissolved oxygen (DO) data for the three SBR sets. Predictions of the calibrated model were successfully confirmed using off-line analyses of soluble chemical oxygen demands (COD) and nitrogen dynamic variations, respectively. The simulated results showed that more SMP was generated under aerobic condition than that under anoxic condition, and more nitrate (S (NO)) consumption resulted in less SMP generation, i.e., approximately 7% and 57% less extra carbon source in sets 2 and 3 were required to remove 8% and 58% of S (NO), respectively, compared with set 1. And the kinetics of SSSG process in the proposed model was indirectly validated by comparisons between experimental DO profiles and simulations. Therefore, the new model provides an effective technique for better optimizing the effluent COD and nitrogen with low energy cost in biological wastewater treatment plants.