Compared with other diseases, severe acute pancreatitis has a certain regularity in the course of the disease. The whole course of the disease can be roughly divided into 3 phases. 1, acute reaction period: from the onset to about 2 weeks, characterized by a systemic inflammatory response, often accompanied by major complications such as shock, acute respiratory distress syndrome (ARDS), acute renal failure and pancreatic encephalopathy. In addition to abdominal pain and distension, patients in this period also have impairment of other organ functions throughout the body. Patients may present with fever, shortness of breath, dyspnea, rapid heart rate, decreased blood pressure or even shock, oliguria or even anuria, gastrointestinal bleeding, irritability, babbling or even coma, etc. Treatment in this stage is usually carried out in the ICU with close monitoring and strong organ function support, and some patients need tracheal intubation (incision) with ventilator-assisted breathing, or the need for blood purification therapy, and some patients require emergency surgery. Due to the development of the disease process itself, the patient’s condition can still gradually worsen after admission, and even multi-organ failure may occur, and a small number of patients may die in this stage. 2. Systemic infection period: After the patient has passed the acute phase, the systemic condition will gradually improve and there will be a short period of “stable condition”. However, at this time, it cannot be considered that pancreatitis has been cured. At this time, there are more or less local complications in the peri-pancreatic area, such as: peri-pancreatic fluid, necrotic infection, peri-pancreatic abscess, bleeding and so on. In some patients, local complications do not require special treatment and can be cured by self-absorption under close observation; in some patients, they can be cured by puncture and drainage; in some patients, complications such as infection, abscess, bleeding, intestinal fistula, etc. need to be treated by caesarean operation. Due to the special nature of pancreatitis, continuous flushing and drainage for 1-2 months (or even longer) is usually required after surgery. Some patients can develop complications such as hemorrhage, abscess and intestinal fistula after surgery, sometimes requiring multiple surgical treatments, and a few patients can develop fungal infection, multi-organ failure, or even death. 3, residual infection stage: the time is 2-3 months later, mainly manifested by general malnutrition and the presence of posterior peritoneum or residual abscess in the abdominal cavity. Not all patients have a 3-stage course, some have only the first stage and some have the second stage.