Pre-operative radiotherapy for gastric cancer can kill cancer cells, reduce the size of cancer tumor, and improve the surgical resection rate; 2. kill or inhibit the invasion of cancer cells on the plasma membrane surface, prevent intraoperative dissemination and implantation, and improve the surgical cure rate; 3. occlude the vasculature and reduce the chance of cancer cells metastasizing and spreading from lymphatic vessels or blood vessels; 4. eradicate subclinical lesions in the irradiated field. Indications for preoperative radiotherapy for gastric cancer: (1) Stage II and III gastric cancer is the main target; (2) Preoperative radiotherapy is appropriate for pathological types Borrmann I and II, and some types III can be treated with radiotherapy, but type IV is not suitable for preoperative radiotherapy because it often involves the organs on all sides; (3) Preoperative radiotherapy is appropriate for tumor diameter below 6 cm, and the effect of radiotherapy is poor for cases over 10 cm; (4) Radiotherapy is effective for undifferentiated or low (4) radiotherapy is very effective for undifferentiated or low differentiated adenocarcinoma.