We establish a three-dimensional tidal current mathematical model，verify the model by the measured tidal level and stratified velocity and flow direction data，carry out simulation study on the tidal current distribution of the east and north breakwater extension scheme of Dagukou Port area of Tianjin Port. The results show that the velocity distribution of the surface layer near the port area is basically the same as that of the 0.6h water depth，the velocity of the bottom layer is obviously smaller，and the velocity direction of each layer is relatively consistent. Under the condition of port entrance current layout，the velocity and cross flow near the gate are relatively large. After the implementation of the extension project of the breakwater in the east and north of the entrance，the flow pattern near the entrance channel is obviously improved，and the cross flow velocity is also obviously reduced. Considering the improvement of flow conditions，the extension scheme is suitable.