Abstract: In order to improve TN removal rate of leachate, the anaerobic sequencing batch reactor (ASBR) combined with the improved sequencing batch biofilm reactor (SBBR) process was used to treat the actual municipal solid waste (MSW) leachate with chemical oxygen demand (COD) of (5 700±500) mg/L and TN concentration of (210±50) mg/L. The results showed that the effluent of ASBR entered SBBR reactor for deep denitrification, and the main function was to adjust C/N of subsequent SBBR influent, and the removal rate of COD in leachate was 90%. C/N was the key to determining the nitrogen removal efficiency of SBBR. After adjusting the influent C/N to 4.8, under the action of biofilm, the deep denitrification of MSW leachate could be achieved only by anaerobic stirring and simultaneous nitrification and denitrification (SND) in the aerobic stage. The effluent total nitrogen concentration was lower than 10 mg/L, and the cycle running time was shortened from 24 hours on the 54th day to 5.6 hours. The best treatment effect could be achieved after 103 days of domestication and start-up of the whole system. The concentrations of COD, NH₄ ⁺-N and TN in the effluent were (380±10), (1.0±0.5) and (5±5) mg/L, respectively, and the removal rates were more than 93%, 99% and 95%, respectively. Through high-throughput sequencing analysis, the relative abundance of Proteobacteria and Bacteroides in the system was high, with 55.11% and 21.32%, respectively. In the system, the abundance of Firmicutes with denitrification accounted for 2.81%, which may be the key to achieving an excellent denitrification effect in SBBR. At the genus level, the bacteria with denitrification function in the system were mainly Thauera and Limnobacter, accounting for 15.22% and 2.84%, respectively. Their existence may be one of the main reasons for the good effect of the system SND. The system achieved deep denitrification of leachate without adding any carbon source and had high nitrogen removal efficiency, which provided an effective way for MSW leachate to meet the discharge standard of total nitrogen.