In order to study the degradation of nitrogen in the process of purifying tailwater of mariculture by integrated vertical-flow constructed wetland system, the degradation characteristics of TDN, DON and three forms of DIN in the constructed wetland system were simulated using the first-order kinetic model, and the relationship between nitrogen degradation and the community structure and composition of microorganisms in the system was analysed by the PCR-DGGE technique. The results showed that the degradation of various forms of nitrogen in tailwater of mariculture conformed to the first-order kinetic characteristics (R2≥0.70), with the degradation rate in the order of DIN> TDN> DON, and the removal rate constant of 0.10h-1, 0.09h-1 and 0.03h-1 respectively; among the components of DIN, the degradation rate was in the order of NH4+-N> NO2--N> NO3--N, and the removal rate constant was 0.15h-1, 0.11h-1 and 0.09h-1 respectively . Bacteria related to denitrification were rich in the substrate layer and around the plant roots, indicating that microorganisms played a vital role in the nitrogen removal process. Among them, the main dominant bacteria were Proteobacteria (34.46%), Cyanobacteria (12.78%), Actinomycetes (10.55%), Campylobacter (10.46%) and Bacteroides (7.78%). The research results will provide a theoretical basis for revealing the nitrogen removal mechanism in seawater constructed wetlands.