The common chemotherapy regimen includes fluorouracil combined with calcium folinic acid. In case of obvious distant metastasis or advanced rectal cancer, oxaliplatin can also be combined and administered in different ways, either as a 5-day injection or as a 3-week pump injection. If the previous regimen is not effective, irinotecan can be replaced with intravenous chemotherapy in combination with calcium folinic acid and fluorouracil. Because of the side effects of irinotecan, especially gastrointestinal reactions, care should be taken during the treatment period to protect the liver and kidneys, to protect the mucosa of the gastrointestinal tract and to monitor changes in liver and kidney function indicators.