The microorganisms of the body are mainly distributed in the human body surface, respiratory tract, digestive tract, urethra, vagina and other organs that are connected to the outside world. Among them, the skin, oral cavity, intestinal tract, vagina is known as the human body’s four major bacterial reservoir. The human body contains a huge number of microorganisms. Different parts of the distribution of different microorganisms, different parts of the microbes have different physiological functions. 1. Skin: the flora is mainly composed of staphylococci, Pseudomonas aeruginosa, Propionibacterium, Mycobacterium, etc. As the first barrier of the human body, it plays an important role in thermoregulation and nutrient metabolism of the skin. 2. Oral cavity: composed of Porphyromonas, Streptococcus, Clostridium, Lactobacillus, Pseudomonas albicans, Actinobacillus and so on, which can protect the oral cavity from pathogens and maintain our oral health. 3. Intestinal tract: contains the most microorganisms, consisting of Escherichia coli, yeast, spirochetes, Lactobacillus and a small number of cocci, etc. These flora are mainly planted in the large intestine, and play an important role in maintaining the intestinal barrier function, enhancing immunity, providing energy for the intestinal mucosa, and synthesizing vitamins. 4. Vagina: composed of Lactobacillus, Escherichia coli, Pseudomonas albicans, etc. It plays an important role in maintaining the self-purification of the female reproductive tract, maintaining the acidic environment of the reproductive tract, resisting the colonization of pathogens, and enhancing immunity. Microorganisms, host and external environment constitute a dynamic ecological balance, which is very important for the health of the body.