Abstract: In this paper, a three-dimensional hydrodynamic model of Maniao Bay was established and verified with measured data such as water level, flow velocity and flow direction, and the flow field characteristics of Maniao Bay at different characteristic moments were analysed, In order to assess the water exchange capacity of Maniao Bay, a water exchange correlation matrix model was established, and the water exchange period between the Maniao Bay and the outer sea was calculated. In order to find out where the seawater in the aquaculture area comes from and where it goes, Maniao Bay was divided into 12 sea areas including the aquaculture area, and the water exchange period of each sea area in the bay were calculated. The results showed that: the flow velocity at the mouth of Maniao Bay is significantly higher than that in the bay, with a maximum flow velocity of about 1.1 m/s. A distinct counterclockwise vortex is formed during ebb tide, conversely, a clockwise vortex is formed during flood tide in the bay. The water exchange capacity of spring tide between Maniao Bay and the outer sea is greater than that of neap tide, the average half-exchange period of the spring tide is about 8.2 h, whereas the half-exchange period of the neap tide is about 21.1 h. The mouth of the bay has the strongest water exchange capacity, and the half-exchange period is less than 1h. The most significant exchange of seawater between the aquaculture area and the adjacent outer sea but almost no exchange with the bottom of Maniao Bay. This indicates that the site selection of the aquaculture area is reasonable.