This study inoculated aerobic granular sludge (AGS) in a sequencing batch reactor (SBR) treatment for low carbon nitrogen (COD/N) ratio wastewater, and gradually reduced the DO concentration in order to achieve the rapid startup of the simultaneous nitrogen and phosphorous removal (SNPR) process. Meanwhile, the microbial community dynamics at different DO levels were analyzed by high-throughput sequencing. The removal efficiencies of total nitrogen (TN) and phosphorus (TP) were significantly affected as different dissolved oxygen (DO) concentrations (2.0,1.2 and 0.8 mg/L) in stages I, II and III, respectively. When DO concentration was reduced to 0.8mg/L (stage III), the SNPR process was successfully implemented and the removal efficiencies of TN and TP were up to 77.30% and 85.78%, respectively. A total of 40,983 effective 16S rRNA gene sequences were generated from four samples (1-4) that widely represented microbial community diversity. The dominant phyla transformed from Candidate_division_TM7 (the relative abundance of 68.08%) and proteobacteria (25.78%) to Firmicutes (47.57%) and proteobacteria (41.49%) when DO concentration was decreased from 2.0 mg/L (stage I) to 0.8 mg/L(stage III). Moreover, Kluyvera, Peptostreptococcaceae_incertae_sedis, Clostridium_sensu_strict_1, Trichococcus, Denitratisoma, Clostridium_sensu_stricto_13 and Raoultell were the most abundant genus in the SNPR process. Among these communities, Clostridium_sensu_strict_1, Clostridium_sensu_stricto_13 and Denitratisoma were considered the main organisms responsible for simultaneous nitrogen and phosphorus removal.