Most of the existing chemotherapeutic drugs have toxic effects on the normal cells of the body while inhibiting or killing tumor cells, especially the bone marrow hematopoietic cells, and thus myelosuppression occurs during chemotherapy, which can be manifested as a decrease in leukocytes, especially granulocytes, followed by a decrease in platelets and, in severe cases, hematocrit. The degree of myelosuppression varies among drugs, and the speed of recovery also varies. In addition to the type of drug, it is also related to the dose used, the drug regimen and route of administration, the patient’s general condition and the bone marrow reserve status. Therefore, routine blood tests should be performed once or twice a week during chemotherapy to keep abreast of the patient’s bone marrow hematopoietic function and the inhibitory effect of drugs on bone marrow, which can be used as the basis for adjusting the drug regimen.