Under normal circumstances, the daily intake and discharge of water and electrolyte, as well as the quantity, composition and electrolyte concentration of body fluids are in dynamic balance, so as to maintain a relatively stable internal environment, which is called water-electrolyte balance, which is necessary for normal physiological activities of the human body. Water, electrolyte and protein make up body fluids. Body fluid can be divided into intracellular fluid (which directly affects cell metabolism and its physiological function) and extracellular fluid (which circulates continuously in the body to communicate between tissues and cells, and between the body and the outside world). Water is the main component of body fluid, which is not only a good solvent, but also can promote metabolism, participate in various chemical reactions, reduce the proportion of nutrients, absorb, operate and discharge metabolic wastes, and regulate body temperature. Adult males account for about 60% of the body weight, and females account for about 55%. There are many kinds of electrolytes in body fluids, but the amount is very small. The most important are sodium, potassium, chlorine, calcium and magnesium. Their important functions are to maintain the volume, osmotic pressure, acid-base balance and neuromuscular stress of body fluids and participate in the metabolism of various substances. The daily drinking water of normal adults is generally about 2500ml, and the daily requirements of main electrolytes are: sodium (converted into sodium chloride) 10 ~ 15g, and potassium chloride 3 ~ 5g. The intake of water and electrolyte varies greatly among individuals, which is mostly related to food types, personal habits, climatic conditions and activities. Water and electrolytes needed by normal people are ingested through the oral cavity and excreted through four channels: kidney (urine), gastrointestinal tract (feces), lung (breathing) and skin (sweat), among which kidney plays the most important role. The maintenance of water and electrolyte balance depends on the control and regulation of nervous and endocrine systems. However, when the human body has abnormal intake or discharge, abnormal loss and abnormal neuroendocrine regulation in some cases, water-electrolyte imbalance will occur. Such as long-term fasting, massive vomiting and diarrhea, serious systemic infection, extensive burns, digestive tract fistula and so on. It is prone to imbalance between water and electrolyte.