Abstract: Aquaculture vessels are a new way to expand deep-sea aquaculture. How to improve the utilization efficiency of aquaculture tanks to ensure the best growth conditions for fish in aquaculture tanks and the efficient discharge of particulate matter from the tanks will affect the productivity of aquaculture and the profitability of aquaculture vessels. In order to investigate the influence of the diameter to depth ratio of the tanks on the flow field characteristics and the drag coefficient of the tanks, as well as to provide a reference for the structural design and optimization of aquaculture tanks on aquaculture vessels, we carried out an experiment of the flow field characteristics of the tanks of aquaculture platform under mooring condition by using a real-ship test method. We evaluated the influence of the diameter to depth ratio on the fishability and energy loss of the tanks by studying the flow velocity, drag coefficient and the uniformity index of flow field, etc. The experimental results show that the flow velocity in the tanks was positively correlated with the diameter to depth ratio: when the diameter to depth ratio was less than 1.6∶1, the reduction of the diameter to depth ratio led to a significant reduction of the flow velocity in the tanks, and the tanks with a diameter to depth ratio of 1.8∶1–2.0∶1 possessed better flow characteristics, including higher flow velocity, flow uniformity and lower drag coefficient; a diameter to depth ratio of 1.8∶1 for the aquaculture tanks met the requirements of flow field and economic efficiency in the tanks, and this ratio should be considered as a priority in the aquaculture system of aquaculture vessels.