Abstract: Water environment with high density of fish feeding was simulated under Biotron Open Type and natural condition in Jingzhou of Jianghan Plain, and day-night aquaculture water observation of DO (dissolved oxygen) and water temperature variation were carried out by using water quality multi-parameter monitoring system in a totally open way. Dynamic balance formula was used to calculate water-atmosphere DO rate, oxygen production of photosynthesis, oxygen consuming rate of grass carp and water body; grass carp survival time under low oxygen condition was also observed. The result shows that, oxygen consuming rate of water body in pool is 1.22-1.83 mg/(L·h), while oxygen consuming rate of grass carp is 78.6-210.0 mg/(L·h) when water body DO is above 1.5 mg/L. The oxygen consuming rate of aquaculture ponds in high density fish feeding environment is more than 4 times of the oxygen consuming rate of fish. The oxygen dissolution rate of water-atmosphere interface is low. And oxygen production of photosynthesis is 3.47-4.33 mg/(L·h) in rainy or cloudy days, which is more than the total oxygen consuming rate of fish and aquaculture ponds, while oxygen production of photosynthesis in rainy days cannot maintain favorable environment in aquaculture ponds. The grass carp would gasping for air but still survive 5 more days in low DO environment as 0.1-0.4 mg/L. The result also indicates that lacking oxygen could cause the increase of H₂S and CH₄ in the bottom of aquaculture ponds; water convection in aquaculture ponds and increase of toxic substances caused by rain is the main reason of suffocation.