After the qualitative diagnosis of gastric cancer is obtained through gastroscopy and biopsy, the next step is to perform relevant imaging examinations with the aim of quantitative diagnosis (TNM staging), therefore, the diagnostic reports of various imaging examinations should reflect the concept of TNM staging, focusing on the depth of infiltration (T), lymph node metastasis (N) and distant metastasis (M) status. Staging diagnosis is the main evidence for resectability assessment and treatment selection: 1. Preoperative staging diagnosis mainly relies on ultrasound gastroscopy and enhanced abdominal CT. ultrasound gastroscopy can help evaluate the depth of infiltration (T) and perigastric lymph node metastasis (N) status of gastric cancer and is recommended for preoperative staging of gastric cancer. Ultrasound gastroscopy is mandatory for patients who are proposed to undergo reduction surgery such as endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD). The sensitivity and specificity of ultrasound gastroscopy is better for T1 to T3 and N1 stage cases, but it is not as good as abdominal enhancement CT for T4a and N2 stage or above cases. 2. Abdominal enhancement CT is a routine method for preoperative staging of gastric cancer. CT examination of stomach must be scanned in the state of gastric filling and hypotension; if the stomach is poorly filled and the stomach wall is wrinkled, no accurate judgment can be made. A good abdominal enhancement CT can accurately determine the lesion extent and infiltration depth of gastric cancer, the metastatic status of perigastric lymph nodes, and the relationship between tumor and surrounding organs. Female patients should have additional pelvic enhancement CT/ultrasound. 3. Chest X-ray examination used to be a routine method for preoperative staging, but now it is increasingly replaced by chest CT. The purpose is to understand the presence of pulmonary metastases and other pulmonary lesions. Chest X-ray must be taken with both frontal and lateral chest films. 4.MRI examination is not recommended as a routine examination. MRI may be considered for patients who cannot do enhanced CT examination due to allergy, or who are suspected of peritoneal metastasis or intra-abdominal dissemination by CT examination, or who are proposed to have neoadjuvant therapy. 5. PET/CT is not recommended as a routine examination. PET/CT scan can be considered for patients in whom CT and MRI cannot identify or exclude peritoneal metastasis or intra-abdominal dissemination. 6, laparoscopic exploration and free cytology of the abdominal cavity are not recommended as routine examinations and can be used mainly to evaluate the presence or absence of peritoneal dissemination, and are recommended for patients with cT3 or higher. 7. Biopsy is not necessary for patients with imaging diagnosis of distant organ metastases, such as multiple lung metastases, brain metastases, liver metastases, bone metastases, etc.