On the basis of the hydrological data obtained from fixed-point observation in the mouth area of Xiashimen strait channel from May 10 to 19,2015(from neap tide to spring tide),the hydrodynamics characteristics and transport mechanism of water are analyzed using the method of harmonic analysis,mathematical statistics and decomposition mechanism.The results show that:the nature of tides is moderate intensity non-regular semidiurnal shallow sea tide;the characteristic of tidal wave is similar to that of typical forward wave;the form of tidal current is in the transition zone of the reversing current to rotational flow,and the tides rotate in a clockwise direction.The vertical distribution of tidal current velocity decreases from the surface to the bottom,and the maximum flow rate appears in the surface layer or 0.2H layer;the average vertical velocity shows spring tide＞neap tide＞mean tide; the flood current is dominant in the water,and tide dominant flow decreases from neap tide to spring.Water transport power bases on Euler residual current,and shows spring tide＞neap tide＞mean tide.