The nitrogen may cause eutrophication in water bodies. Monitoring and controlling the concentration of total nitrogen in water bodies is the key to ensuring the safety of the water environment. The total nitrogen content in the water body includes nitrogen in nitrite nitrogen, nitrate nitrogen, inorganic ammonium salt, dissolved ammonia and most organic nitrogen compounds. According to environmental protection requirements, total nitrogen online analyzer has been widely used in surface water and pollution source on-line monitoring. This paper summarizes the current status and future development of total nitrogen online automatic monitoring equipment, introduces the basic principles of total nitrogen detection, water sample treatment and digestion methods, analyzes and compares the technical indicators of water quality total nitrogen automatic online monitoring equipment. According to china's water environment governance development, the total nitrogen automatic online monitoring technology and instrument should be development. This paper provides reference for the development and industrialization of related instruments.