A pilot modified four step-feed process was applied to deal with weak municipal wastewater. After 133 days of continuous operation with different hydraulic retention time(HRT) and operation strategy， the results are obtained as the following: (1)When HRT is reduced from 8.7h to 6h， there is almost no effect on performance of COD and TP， but would lead to increase effluent NH4 +-N and TN. Meanwhile， the influent carbon source utilization and simultaneous nitrification and denitrification (SND) are correspondingly decreased. (2)When HRT is 6h， the DO concentration in areobic zones are controlled between 1.0-1.5 mg·L -1 and adding suspended carriers in aerobic zones， the effluent performance of COD， NH4 +-N， TN and TP are 25.92， 1.98， 14.5and 0.47 mg·L -1 respectively. (3)Suspended carriers can be used to optimize the effluent ammonia and SND performance， and achieve 22% of TN removed through SND with suspended carriers. However， it's not obvious for suspended carriers to improve the influent carbon source effective utilization.