Abstract: Based on an unstructured grid and finite-volume coastal ocean model that contained eight main tidal components of K₁、O₁、P₁、Q₁、M₂、S₂、N₂ and K₂, this paper developed a three-dimensional hydrodynamic model with high-resolution in Dalian bay of China.By comparing the simulated elevation and current data with the observed data, the model could well reflect the hydrodynamic characteristics.Furthermore, DYE-RELEASE module was merged into model to simulate water exchange process and half-life time was used to evaluate the capacity of the whole and sub-regions of Dalian bay.The simulation results indicates that, initial time of tracer release has an impact on the half-life time.On the average, half-life time is 9.6 d~12.3 d in Dalian bay.The concentration decreased more rapidly in spring tide period than in neap tide period so that water exchange capacity in spring tide period is stronger.The half-life time distribution is characterized by the shorter distance from the mouth to the bay and the shorter half-life time.Under the same distance, the half-life time of the southwest is shorter than that of the northeast.The water exchange capacity is characterized by that, the strongest is the central part of Dalian bay, followed by Hongtuduizi bay and the weakest is Tianshuitao and Choushuitao bays.