<p>Under the assumption of the constant flux layer, Monin-Obukhov Similarity Theory (MOST) is widely employed to relate wind stress to mean wind profiles. However, by summarizing several observations, this paper finds that the behavior of wind profiles close to the surface differs from that predicted by MOST, which is larger than that estimated by MOST under wind sea conditions and smaller than that for swell cases. The wave coherent stress computed from the widely used traditional vertical decay function is almost one order of magnitude smaller than that derived from observations. A coupled model based on the shear instability with an “arbitrary” wind profile is used to investigate the above phenomena. The result shows that the deviation of the wind profile from MOST is due to the wave coherent stress that considers parts of the total stress. Thus, accurate determination of the wave effect height or the height to which wave coherent stress can extend is very important in air-sea interactions. Our model suggests that only those wave modes that have phase speeds greater than <i>U</i>(<i>z</i>) can extend their stress higher than <i>z</i>, here <i>U</i>(<i>z</i>) is the wind speed at height <i>z</i>. Compared with the traditional vertical decay function, the results of this study are in good agreement with the observed wave coherent stress.</p>