Various aspects of studies on internal tides are reviewed .Both beam-like structure and modal structure of internal tides may exist in the ocean . Bottom intensifications are caused by many factors .e.g. upstream blocking , which is the result of nonlinear interaction among waves . The energy may decay very fast so that internal tides are mostly locally generated .Internal tides may have considerable residual currents.In a 3-D frame, numerical study revealed that internal waves may interfere with each other to cause strong motions fer from the generation sources.The mechanism that determines how the lee waves break to form various nonlinear waves such as solitary waves, hydraulic jumps and internal surges or bores remains unclear. Analytic study is difficult , so numerical method may be effective . A radiation condition on the open boundary must be employed. A complete 3-D model may gain interesting result.Study on internal tides in China is limited to field observations and data analysis . Various aspects of studies on internal tides are reviewed .Both beam-like structure and modal structure of internal tides may exist in the ocean. Bottom intensifications are caused by many factors .eg upstream blocking, which is the result of nonlinear interaction among waves. energy may decay very fast so that internal tides are mostly locally generated. Internal tides may have substantial residual currents. In a 3-D frame, numerical study reveals that internal waves may interfere with each other to cause strong motions fer from the generation sources. The mechanism that determines how the lee waves break to form various waves waves such as solitary waves, hydraulic jumps and internal surges or bores remains unclear. Analytical study is difficult, so numerical method may be effective. A radiation condition on the open boundary must be A complete 3-D model may gain interesting result. Research on internal tides in China is limited to field observations and data analy sis.