Abstract: In this study, a constructed wetland based on pyrite—biochar was constructed to analyze the effect of dissolved oxygen concentration on the tail water treatment effect of mariculture. When the influent dissolved oxygen concentration was 3-5 mg/L and 6-8 mg/L, the TN removal efficiency of the constructed wetland was stable between 20% and 30%. When the concentration of dissolved oxygen in the influent was 0-2 mg/L, the TN removal rate was more than 40%, but the NO₂-N concentration generated was up to 5.07 mg/L, which was harmful to biological health. High dissolved oxygen concentration was more conducive to the removal of phosphate (PO₄-P). When the PO₄-P concentration in the constructed wetland was 33.10 mg/L, the removal rate of PO₄-P in the constructed wetland with dissolved oxygen concentration of 6-8 mg/L was more than 37%. SEM-EDS scanning showed the presence of Fe-P complexes on the surface of pyrite treated with aquaculture tail water, which further proved that the system had some ability to remove P from tail water. The analysis of microbial community composition showed that appropriately increasing the concentration of dissolved oxygen in influent water was conducive to microbial enrichment in pyrite-biochar based constructed wetland. The results showed that the constructed wetland system in this study had a good treatment capacity for tail water of high-dissolved oxygen aquaculture, which provided a theoretical basis for the treatment of tail water of mariculture.