This paper describes the numerical simulations of tidal current and substance dispersion using Finite Element Method. In this paper, two-leveled mathematical models of tidal current and substance dispersion are formulated in order to examine the effect of density stratification, river discharge and wind on flow or substance dispersion. It is assumed that the level of interfacial surface is fixed.
　According to the results of one-layer system and two-layer system, averaged current velocity between upper and lower layers is almost the same as the velocity of one-layer system, in spite of the fact that the current velocity in upper-layer is considerably higher than the velocity in lower-layer.
　The influence of river discharge on current is restricted around the mouth of big river. The wind driven current in upper-layer is about 3 cm/s/10knot to same direction as wind, whereas the water body in lower-layer is driven to opposite direction as the one in upper-layer because of compensation.
　The resutls of contaminated water dispersion and salt water distribution simulations agree well with the field survey data in Tokyo Bay. Vertical current at interface acts vertical mixing of substance or salt between upper and lower layers.