This study explored the denitrification performance of solid-phase denitrification (SPD) systems packed with poly (butylene succinate)/bamboo powder composite to treat synthetic aquaculture wastewater under different salinity conditions (0‰ Vs. 25‰). The results showed composite could achieve the maximum denitrification rates of 0.22 kg (salinity, 0‰) and 0.34 kg NO3−-N m−3 d−1 (salinity, 25‰) over 200-day operation. No significant nitrite accumulation and less dissolved organic carbon (DOC) release (<15 mg/L) were found. The morphological and spectroscopic analyses demonstrated the mixture composites degradation. Microbial community analysis showed that Acidovorax, Simplicispira, Denitromonas, SM1A02, Marinicella and Formosa were the dominant genera for denitrifying bacteria, while Aspergillus was the major genus for denitrifying fungus. The co-network analysis also indicated the interactions between bacterial and fungal community played an important role in composite degradation and denitrification. The outcomes provided a potential strategy of DOC control and cost reduction for aquaculture nitrate removal by SPD.