Pathological tests and genetic tests should be done before chemotherapy for colorectal cancer to help determine the chemotherapy regimen. The main chemotherapeutic agents include folfox4, folfiri, etc. The basic drug used is fluorouracil. There are more types of chemotherapy regimens, including first-line chemotherapy, second-line chemotherapy and third-line chemotherapy. Also, according to the specific situation of patients, if they are not sensitive to chemotherapy drugs, they can seek suitable targeted drugs under the guidance of genetic testing to provide a better treatment direction for patients. The side effects of chemotherapy are mainly myelosuppression, which is manifested as a decrease in white blood cells, platelets, hemoglobin and red blood cells, and fluorouracil can damage the intestinal mucosa.