Dissolved Oxygen refers to oxygen dissolved in water in a molecular state, that is, O2 in water, expressed as DO. Dissolved oxygen is an indispensable condition for the survival of aquatic organisms. One source of dissolved oxygen is when the dissolved oxygen in the water is not saturated, the atmospheric oxygen penetrates into the water body; the other source is the oxygen released by the plants in the water through photosynthesis. Dissolved oxygen changes with changes in temperature, air pressure, and salinity. Generally speaking, the higher the temperature, the larger the dissolved salt, and the lower the dissolved oxygen in water; the higher the air pressure, the higher the dissolved oxygen in water. Dissolved oxygen is consumed not only by reducing substances such as sulfide, nitrite, and ferrous ions in water, but also by the respiration of microorganisms in water and the oxidative decomposition of organic substances in water by aerobic microorganisms. Therefore, dissolved oxygen is the capital of the water body, and it is the expression of the self-purification ability of the water body. The dissolved oxygen in natural water is close to the saturation value (9ppm). When the algae reproduce vigorously, the dissolved oxygen content decreases. Water is contaminated with organic and reducing substances, which can reduce dissolved oxygen. For aquaculture, dissolved oxygen in water has a crucial effect on the survival of aquatic organisms such as fish. When the dissolved oxygen is less than 4mg / L, It can cause suffocation of fish. For humans, the content of dissolved oxygen in healthy drinking water should not be less than 6mg / L. When the consumption rate of dissolved oxygen (DO) is greater than the rate of oxygen dissolved in water, the content of dissolved oxygen can approach 0. At this time, anaerobic bacteria can multiply and deteriorate the water body, so the size of dissolved oxygen can reflect the water body Pollution, especially the degree of organic pollution, is an important indicator of the degree of water pollution and a comprehensive indicator of water quality. Therefore, the measurement of dissolved oxygen content in water bodies is of great significance for environmental monitoring and the development of aquaculture.