It is well known that the solution of linear shallow-water equations subject to the boundary conditions consists of incoming and reflected Kelvin waves as well as one or more Poincare modes. Generally, Poincare mode decays away from the boundaries. However, if the width become large or depth becomes small beyond the critical values, the Poincare mode can co-exist with Kelvin wave and become important (Hendershott and Speranza,1971). This is the case for the tidal regime within a zone of the northern Jiangsu province whereby Poincare wave appears due mainly to the sudden expansion of the lateral extent through the Korea Strait opening. The shallow Yangtze River Shoal in the south Yellow Sea also contributes to its existence. The Poincare waves, trapped in a transition zone coinciding with the width of the Korea Strait, play an important role in modulating the regular M2 tide especially in the shallow region. The numerical tidal model set up in the Yellow Sea demonstrated that the modulation of the M2 tide in the form of Stoke’s drifts resulting in a radial tide pattern near Jianggang, Jiangsu, China.