Based on over 8 years of moored observation data near the Xisha Islands in the South China Sea (SCS), this study investigated the seasonal variability and vertical distribution of near-inertial waves (NIWs) and internal tides (ITs). It also investigated the impact of mesoscale cyclonic eddies on the downward propagation of NIWs, as well as the mechanism of nonlinear interactions between NIWs and ITs following typhoons. Both NIWs and ITs exhibited significant seasonal variations. Near-inertial kinetic energy (NIKE) was stronger in autumn and winter, while internal tide energy peaked in both summer and winter. Over the entire observation period, ITs were primarily dominated by low modes. In contrast to internal tides, which are dominated by low modes, NIWs exhibit high-mode structures under the influence of negative vorticity. During periods of positive vorticity, the modal structures of NIWs show significant variability. In addition, the study found that cold eddies can also facilitate the downward transfer of near-inertial energy. Taking the autumn of 2011 as an example, under the influence of positive vorticity, NIKE was transmitted downward to the maximum observed depth of 543m, contributing to deep-ocean mixing. The study also revealed that typhoon-induced NIWs, characterized by strong vertical shear, played a dominant role in the nonlinear interactions between NIWs and ITs, leading to the enhancement of nonlinear coupled waves.