The criteria for the classification of surgical grades are mainly based on the complexity and risk of the surgery, and are generally categorized into one to four grades. 1. Level 1: refers to various surgeries with relatively simple procedures, low risk and low surgical difficulty. For example, open and closed chest drainage, arterial and venous cannulation, and general debridement and tendon repair belong to this type of standard surgery. 2. Level II: refers to various surgeries that are not very complicated, with moderate risk and relatively normal difficulty. For example, uterine laceration repair and vasectomy anastomosis belong to this standard surgery. 3. Level 3: This standard surgery is relatively more complicated, the risk factor and difficulty of the surgery is also relatively large, and the requirements for doctors are also higher. Such as endoscopic mucosal resection. 4. Level 4: This standard surgery, the operation process is complex, the risk factor and difficulty are very large, the patient and the doctor is a great test. For example: intracranial aneurysm clamping and embolization, thoracic aortic aneurysm and abdominal aortic aneurysm surgery, lung transplantation, combined heart and lung transplantation.