It is of practical significance to investigate shallow water tides sinec there is a vast expanse of shallow sea surrunding our eastern border in the cast. In this paper for the study of tidal waves in ahalIow water we present a three-dimentional nonlinear model. On the basis of tidal constituent concept, the model dosigned could be used not only for the detoction of astronomical tides but also for aifferent orders of shallow water comstituents. For the jta order of constinents (as defined in the present artiele), the boundary value problews of elliptie differential equations for the tidal elevation are derived; in addition, the analytical expressins of the vertical distribution for tidal corrents are deduced.