Two-level numerical models are formulated to predict the flow pattern, SS(suspended solids) distribution and the behavior of discharged fresh water in estuary, and are applied to the Suyoung River estuary in Pusan, Korea. To verify the application of the models, field observations of tidal current, salinity and 55 were performed during the period of spring tide. Computed upper level velocities by two-level model are in better agreement with observed values than single model. Apart from the magnitude of the velocities, the predicted flow fields at upper level are similar to those obtained at lower level. Upper level velocities in river channel during ebb spring tide are about 2 times stronger than those during flood spring tide due to the discharging flow rate from the Suyoung River. Two-level model results on the salinity and 55 distribution at upper level are compared with the observed ones at the surface. Computed salinity distributions are in good agreement with the observed values, but computed 55 distributions show $6{~}10$ ppm higher values than the observed ones.