It is an indispensable substance around our life, but with the development and progress of human life, the surface and groundwater bodies are polluted and the water quality deteriorates. It not only makes the limited water resources more tense, but also if people use the polluted water resources, it will directly affect their physical and mental health. Therefore, what the relevant staff have to do is to monitor the water quality online, which is of great significance to everyone. Water quality monitoring is the process of monitoring and measuring the types of pollutants in the water body, the concentration and change trend of various pollutants, and evaluating the water quality status. The scope of monitoring is very wide, including unpolluted and polluted natural water (river, river, lake, sea and groundwater) and various industrial drainages. The main monitoring items can be divided into two categories: one is comprehensive indicators reflecting water quality, such as temperature, chromaticity, turbidity, pH value, conductivity, suspended solids, dissolved oxygen, chemical oxygen demand and biochemical oxygen demand etc.; the other category is some toxic substances, such as phenol, cyanide, arsenic, lead, chromium, cadmium, mercury and organic pesticides. In order to objectively evaluate the water quality of rivers and oceans, in addition to the above-mentioned monitoring items, it is sometimes necessary to measure the flow velocity and flow. Another: The scope of water quality monitoring is very wide, including regular surface and groundwater monitoring, surveillance production and living process monitoring, and emergency accident monitoring. Water quality monitoring can provide data and information for environmental management, and can provide a basis for evaluating the water quality of rivers and oceans. 1. Regular monitoring of surface water and groundwater. 2. Surveillance monitoring of production and life processes. 3. Accident monitoring Emergency monitoring. 4. Provide data and information for environmental management. 5. Provide data and information for environmental science research.