Defective immune function of the body’s defense is the most important causative factor of sepsis. In healthy individuals, after the invasion of pathogenic bacteria, generally only transient bacteraemia is manifested, and the bacteria can be rapidly eliminated by the body’s immune defense system and do not cause obvious symptoms; however, people with various immune defense defects (including the loss of local and systemic barrier function) are prone to sepsis. 1, various causes of neutrophil deficiency or reduction is an important cause of sepsis, but the incidence of sepsis is significantly higher when neutrophils fall below 0.5×109/L, mostly in patients with acute leukemia, after bone marrow transplantation, after chemotherapy in patients with malignant tumors, and in patients with aplastic anemia. 2. Immunosuppressants such as adrenocorticotropic hormone and broad-spectrum antibiotics, radiation therapy, application of cytotoxic drugs, and various major surgeries are important triggers of sepsis. 3, tracheal intubation, tracheotomy, application of artificial respirator. Retention of intravenous catheters, intra-arterial catheters, retention of urinary catheters; burn wounds. Various intubation examinations, such as endoscopy, intubation angiography or placement of internal drainage tubes, etc. can destroy the local barrier defense function and facilitate the invasion of pathogenic bacteria. 4. Serious primary diseases, such as cirrhosis, connective tissue disease, diabetes mellitus, uremia, and chronic lung disease, are also causative factors for sepsis. Smear examination and culture with pus, cerebrospinal fluid, thoracoabdominal fluid, bruising point squeeze field, etc., also have the opportunity to detect pathogenic bacteria. The pathogenic bacteria can be isolated for post-sensitivity testing to determine the minimum inhibitory concentration (MIC) for reference in the selection of antibacterial drugs. If necessary, measure the minimum bactericidal concentration (MBC), serum bactericidal test also has important reference significance. General medium without bacterial growth, suspected of L-type bacterial sepsis, hypertonic saline culture should be made. Fungal growth is slow and the culture positivity rate is low. Latex agglutination test to determine the antigen or the corresponding antibody (for cryptococcosis), as well as pathological tissue examination are helpful for diagnosis. The isolation and culture of anaerobic bacteria also takes at least 1 week, which cannot provide a bacteriological basis for clinical treatment in a timely manner. In recent years, rapid diagnostic techniques such as gas chromatography and ion chromatography have been developed. Chromatography can also make the diagnosis of the presence or absence of anaerobic bacteria within 1 hour for the forest mounted specimen, which is convenient to guide the use of drugs. Immunofluorescence method is rapid, sensitive, and can specifically identify anaerobic bacteria; other still have immunoenzymatic phenotypic histochemistry rapid identification of Clostridium perfringens, etc., has a good effect on early diagnosis.