Abstract: Large-scale deep-sea aquaculture platforms contain aquaculture tanks equipped with water circulation systems, forming drainage vortex rotating around the vertical axis. Such phenomena can be observed in a bathtub during its draining process and is therefore named as bathtub vortex. Under the excitation of ocean dynamical environment, sloshing occurs in the tanks on board, leading to hydrodynamical influence upon the bathtub vortex flow field, which is likely to disturb the velocity distribution inside the tank. However, the velocity distribution is closely related to the breeding environment of the fish, hence the flow field characteristics generated by the coupling of sloshing and drainage vortex flow, especially its flow structure andstatistical characteristics need to be investigated and analyzed. In this study, we investigated the flow field characteristics ofthe tank roll sloshing excitation by numerical simulation. And by comparing the flow field characteristics of a stationary water-circulating tank, a sloshing-only tank with no water circulation and a water-circulating tank with sloshing, we revealed thecoupling effects of the vortex flow and sloshing, including the torsion of the central vortex structure, the asymmetry of thevelocity field, and the generation of helical waves on the free surface. Besides, we investigated the effects of the period and amplitude of the sloshing on the flow field through a series of simulations of sloshing conditions with different periods and amplitudes. The results show that: 1) For small-amplitude state, within a certain frequency range, the influence of the sloshingincreased with frequency. 2) For long-period state, the influence of the sloshing increased with amplitude. Furthermore, besides the normal sloshing states, we conducted investigations on some extreme conditions such as small-period and large-amplitude states. Analyses of average velocity and turbulence statistical parameters, etc. show the differences in the vortex destruction mechanisms between the small-period and large-amplitude sloshing conditions. When the sloshing frequency approached the characteristic frequency of the water tank, the strong coupling between the sloshing and water circulation led to severe breaking at the free surface, with a tendency for unidirectional waves to develop into rotational waves; in a long-period state, when the amplitude of the sloshing increased to a certain extent, the sloshing gradually became the dominant factor, hence the vortex flow was disrupted, but with no tendency for rotational waves or breaking of the free surface.