With the ongoing rapid development of China’s mariculture industry, there has been a corresponding surge in the discharge of marine aquaculture tailwater, and the residual bait, feces, and other residues contained in this water have contributed to serious increases in the levels of nitrogen pollution. The wide geographical distribution of maricultural operations and the high concentrations of ions in tailwaters contribute to difficulties in the effective treatment and purification of this waste water, thereby seriously threatening the quality of the marine environment and the sustainable development of marine fishery resources. In this regard, microbial heterotrophic denitrification technology, which has the advantages of excellent nitrogen removal efficacy and less likelihood of contributing to secondary pollution, has increasingly become a focus of scholars engaged in research on mariculture tailwater purification. In this paper, we outline the mechanisms and advantages of heterotrophic denitrification and denitrification technology, summarize and assess the progress of research and the application of heterotrophic denitrification and denitrification technology in current mariculture tailwater treatment, and describe and evaluate the factors influencing the efficiency of denitrification, including the type of carbon source, hydraulic retention time, temperature, dissolved oxygen, and pH. On this basis of this information, we summarize the difficulties in applying denitrification technology to the commissioning of mariculture tailwater, assess potential solutions to the existing problems, and consider future research directions, with a view toward providing a theoretical basis and technical support for the application of denitrification technology in the efficient treatment of mariculture tailwater.