All level 4 surgeries are major surgeries. Based on the difficulty of the surgery, the types of surgery can be classified as 1-4, of which 1-2 are minor surgery and small and medium-sized surgery, and 3-4 are medium and large surgery. level 4 surgery mainly includes laparoscopic radical treatment of gastric cancer, laparoscopic radical treatment of rectal cancer, laparoscopic resection of liver malignant tumor, laparoscopic resection of pancreaticoduodenum, and radical treatment of thyroid malignant tumor. These surgeries are more traumatic, more complex and have significantly higher chances of serious postoperative complications, and therefore have extremely high surgical requirements for surgeons. Clinically, all level 4 surgeries require a physician of associate chief or above to be qualified to perform them, which shows that level 4 surgeries are major surgeries.