Lacking of electron donor generally causes the low denitrification performance of constructed wetlands (CWs). Montmorillonite supported nanoscale zero-valent iron immobilized in sodium alginate (SA/Mt-NZVI) as novel electron donor-acceptor compounds were added in the denitrification zone of vertical flow constructed wetlands (VFCWs) to enhance the nitrogen removal. The key factors of the SA/Mt-NZVI dosage, the hydraulic retention time (HRT) of VFCWs, and the C/N ratios of influent were explored. SA/Mt-NZVI significantly improved the nitrogen (NO3--N) removal efficiency in VFCWs. When the optimal dosage of SA/Mt-NZVI was set as 2 g and the C/N was set as 6, the highest NO3--N removal efficiency was improved by 32.5 +/- 1.0%. The microbial community analysis of by 16S rRNA had revealed that Proteobacteria and Bacteroidetes at phylum level and Betaproteobacteria, Gammaproteobacteria, and Alphaproteobacteria at class level played an important role in nitrogen removal.