Small cell lung cancer is a malignant tumor of very high malignancy, which is characterized by its tendency to produce recurrence and metastasis. In clinical practice, small cell lung cancer is highly sensitive to chemotherapy. Most patients diagnosed with small cell lung cancer need systemic chemotherapy in clinical practice, and after one cycle of chemotherapy, one cycle is about 21 days, the clinical symptoms will disappear, such as the patient’s cough will be reduced, and the feverish patient’s body temperature will appear to drop. In clinical treatment, usually two cycles of chemotherapy for about 40 days go to evaluate the efficacy of the treatment. If the regimen is effective, 4-6 consecutive cycles of chemotherapy can be administered. If the patient’s disease progresses after the efficacy evaluation, the treatment regimen can be changed and the efficacy evaluation can be continued after two cycles of chemotherapy. Therefore, due to the high sensitivity of small cell lung cancer to chemotherapy in clinical practice, patients are mostly treated for one cycle, i.e., about 20 days, before the efficacy is more apparent.