Summary Body fluid is important component of human body and the physiological equilibrium of body fluid is an important factor for human living. The dynamic equilibrium of fluid, electrolyte, acid-base osmotic pressure depends on normal regulating function of nerve, incretion, lung and kidney. Because of the infantile physiologic peculiarity, These systematic functions are easily affected by diseases and/or environment and are maladjusted Therefore, the disorder of water, electrolyte and acid-base is common in pediatric clinicSummary Body fluid is important component of human body and the physiological equilibrium of body fluid is an important factor for human living. The dynamic equilibrium of fluid, electrolyte, acid-base, osmotic pressure depends on normal regulating function of nerve, incretion, lung and kidney. Because of the infantile physiologic peculiarity, These systematic functions are easily affected by diseases and/or environment and are maladjusted. Therefore, the disorder of water, electrolyte and acid-base is common in pediatric clinic