The ecological floating bed (EFB) coupled with zero-valent iron (ZVI) is proposed to treat low carbon-to-nitrogen ratio water. However, the application of ZVI is limited by low electron transfer efficiency. Coupling ZVI with carbon materials may improve the performance. In this study, the EFB with ZVI coupled plant biomass (IB-EFB) was established to enhance denitrification performance and compared to the EFB with ZVI coupled activated carbon (IC-EFB). The results showed that higher denitrification rate was observed in IB-EFB (68.8%) than that in IC-EFB (54.40%), which attributed to the synergistic effect of ZVI and plant biomass. Plant biomass also promoted the electron transfer of ZVI which enhanced the Fe(II)-mediated denitrification. High-throughput sequencing analysis revealed that IB-EFB enriched iron-related denitrifying bacteria more effectively than IC-EFB, and obtained high abundance of phototrophic Fe(II)-oxidizing bacteria Rhodopseudomonas (19.26%). Thus coupling ZVI with plant biomass has a potential for enhanced nitrogen removal in EFB.