Although radical surgery can remove tumors that are visible to the naked eye and lymph nodes that may have metastases, some tiny tumor tissues or cells that are not even distinguishable to the naked eye cannot be completely removed. The remaining tumor cells can be partially cleared by the body’s immune system, but can recur and proliferate under certain conditions. Numerous studies have demonstrated that post-surgical chemotherapy can reduce the recurrence rate and prolong survival. It must be stated that not all gastric cancers require chemotherapy after surgery. In principle, adjuvant chemotherapy is not necessary after radical surgery for early gastric cancer. However, if it belongs to: 1) pathological type with high malignancy (mucinous adenocarcinoma, indolent cell carcinoma, hypofractionated carcinoma, etc.); 2) the area of cancer foci is relatively large, more than 5 cm2; 3) there are multiple cancer foci; 4) the age is below 40 years. Although the gastric cancer tissue is limited to the mucosa and submucosa, there is still a possibility of metastasis and recurrence in the above cases, and adjuvant chemotherapy should be done after surgery. Those with progressive gastric cancer after radical surgery, after palliative surgery for gastric cancer, or those with recurrence after radical surgery for gastric cancer need chemotherapy. Appropriate amount of chemotherapy for advanced gastric cancer patients can slow down the development of tumor, improve symptoms and have certain recent effects. Patients with gastric cancer should have certain conditions for chemotherapy: they should have clear pathological diagnosis, good general condition, normal heart, liver, kidney and hematopoietic functions, and no serious comorbidities.