Microecological agents in pediatrics recommended as the main drugs used in the disease: 1, diarrhea disease Diarrhea disease is the most clinical application of probiotics and research on the disease, probiotics can be supplemented through the normal intestinal flora, correct the dysbiosis, secretion of bacteriostatic or bactericidal substances and enhancement of the intestinal local immune response to effectively clear the viruses and bacteria and other mechanisms, significantly shorten the duration of diarrhea, reduce the severity of diarrhea, can be used in almost all diarrheal diseases. It can be applied to almost all diarrhea diseases. A large number of clinical and experimental studies have confirmed that the majority of children with infectious diarrhea have intestinal flora disorders. For viral enteritis such as rotavirus, early use of probiotic drugs such as Bifidobacterium, Lactobacillus, Streptococcus faecalis, Clostridium casei, Bacillus and Saccharomyces boulardii is actively recommended. For bacterial or fungal infectious enteritis, a combination of probiotic drugs is recommended based on the administration of sensitive antibiotics or antifungal drugs. Antibiotic-associated diarrhea and diarrhea secondary to pneumonia are mainly caused by intestinal flora disorders, and probiotic drugs such as Bifidobacterium bifidum, Lactobacillus, Streptococcus faecalis, Clostridium casei, Bacillus, and Saccharomyces boulardii are actively recommended for their prevention and treatment. For the prevention and treatment of pseudomembranous enteritis caused by C. difficile infection, Saccharomyces boulardii is supported by more reliable evidence. The etiology of prolonged and chronic diarrheal diseases is complex, but often due to a variety of causes of intestinal flora disorders, in addition to the exclusion of specific causes, it is recommended to use probiotic drugs such as Bifidobacterium, Lactobacillus, Streptococcus faecalis, Clostridium casei, Bacillus and Saccharomyces boulardii. 2.Functional gastrointestinal disorders The etiology of functional gastrointestinal disorders is unclear, and may be related to intestinal motility dysfunction, increased visceral sensitivity, mucosal immunoinflammation, abnormal regulation of the central and intestinal neural axes, and disorders of intestinal flora, etc., and there is a lack of effective treatment. Probiotics have the effect of acidifying the intestinal tract, improving defecation and regulating the intestinal immune-inflammatory response. Probiotic drugs such as Bifidobacterium, Lactobacillus, Streptococcus faecalis, Bacillus subtilis, Clostridium casei, etc. are recommended for functional dyspepsia (including pediatric anorexia), functional constipation, and functional abdominal pain. In addition prebiotic drugs (lactulose) are efficacious and recommended for functional constipation. Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders, and recent epidemiologic studies have shown that some IBS patients occur after acute intestinal infections, and that the onset of IBS is associated with the use of antibiotics; patients with IBS suffer from small intestinal bacterial overgrowth, abnormal colonic fermentation, and intestinal flora dysbiosis. Clinical studies have confirmed the ability of certain probiotics to provide comprehensive relief of IBS symptoms, recommending the use of Bifidobacterium, Lactobacillus, Streptococcus faecalis, Clostridium casei, and Saccharomyces boulardii medications.