Mixed strains Delftia sp.YH01 and Acidovoiux sp.YH02, with capability of heterotrophic nitrification-aerobic denitrification, were introduced into a two-stage aerobic sequencing batch reactor to enhance NO3--N removal. With optimal C/N of 8, efficient NO3--N removal was achieved at initial NO3--N concentration of 2000 mg.L-1. Meanwhile, the massive accumulation of NO2--N was avoided during the long operation. Compared to the one-stage aerobic sequencing batch reactor, the removal efficiency of NO3--N and TN in the two-stage aerobic sequencing batch reactor was increased by 36.5% and 42.7%, which respectively was 93.8% and 88.4%. Microbial community study showed that the mixed strains have the stronger viability and can synergistically denitrify with the indigenous microorganisms in system, such as Azoarcus, Uncultured Saprospiraceae, Thauera, Paracocccus, which could be major contributors for aerobic denitrification. The proposed technology was shown to achieve high-efficiency treatment of high NO3--N wastewater through aerobic denitrification. (C) 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.