ICUs generally have three basic components. ① Trained physicians and nurse practitioners; this is the echelon of ICU personnel. This echelon should master the theory of critical care medicine, have a high degree of resilience, and be good at working together. ②Advanced monitoring technology and treatment tools; with the help of these devices and technologies dynamic and quantitative monitoring can be performed, capturing instantaneous advanced theoretical and technical changes, which can be fed back into powerful treatment measures. ③ It can be applied for effective treatment and care of critical illnesses. Among these three parts, people are the most important component. Advanced equipment is an extension and enhancement of the human audiovisual function and the function of hands, providing more information to the brain and helping people to observe and solve information and difficult problems that were not available in the past. Only in this way can the three characteristics of ICU, namely therapeutic, monitoring and research, be reflected. Critical care medicine is the theoretical basis of ICU work, and physicians are the main body of ICU. A similar unit without doctors can only be called a “specialized care unit” at best, not an ICU. The source of patients in ICU can be divided into four areas. ①Acute reversible diseases: For these patients, ICU can clearly and effectively reduce the mortality rate, and the effectiveness of the treatment is certain. ②High-risk patients: These patients are represented by those who suffer from potentially dangerous underlying diseases but require traumatic treatment for other reasons. ICU can effectively prevent and treat complications and reduce medical costs with certain benefits. ③Acute exacerbation of chronic diseases: ICU can help such patients to pass through the acute phase in the expectation that the patient will return to the original chronic disease state. For this type of patient, ICU may have some benefit. ④Irreversible deterioration of acute and chronic diseases: such as hemorrhage without effective hemostasis, terminal state of malignant tumor patients, etc. ICU cannot give effective help to such patients. These patients are not admitted to the ICU. The treatment of critical diseases should be combined with the control of the primary cause, and the medical work of ICU should be coordinated with the treatment of the corresponding specialties. the treatment of critical diseases in ICU creates the time and possibility for the treatment of the primary cause, so that some diseases that were impossible to treat or impossible to cure can be completely treated. At the same time, the treatment of primary diseases by other specialties is the basis for the fundamental improvement of critical diseases. This organic combination shows the complementarity of critical care medicine and other specialties.