Abstract: The oceanic nitrogen cycle is an important component of the marine elemental cycle, which is driven by different types of microorganisms and is important for assessing the structure and function of marine ecosystems. However, given the coercion of microplastics on marine ecosystems, there is an urgent need to clarify the impact of the presence of microplastics on nitrogen transformation processes in order to improve the understanding of the contemporary and future oceanic nitrogen cycle. Accordingly, this study set different concentrations (0.5% and 0.05%), particle sizes (500 mesh, 150 mesh and 16 mesh), and types (PA, PE, PVC, PP and PS) of microplastics in order to assess whether the presence of microplastics affects the process of nitrogen transformations in the marine sediments as well as in the overlying waters. The results indicate that the presence of microplastics alters the redox environment, which in turn has an impact on the nitrogen cycling process driven by microorganisms. Additionally, it has found that the material type, concentration, and particle size of microplastics have different effects on the nitrogen cycling process, implying that the different properties of microplastics can alters the nitrogen cycling process of marine sediments and the overlying water. Microplastics can affect the nitrogen distribution in the overlying water by influencing the composition and activity of microorganisms in the sediments, posing a challenge to the nitrogen cycle in the water column. Follow-up studies are needed to investigate the isotope dynamics of nitrogen cycling in overlying water under the influence of microplastics in order to improve the understanding of the nitrogen cycle.