Many patients are very aggressive in requesting for hurried surgical treatment after the diagnosis of gastric cancer. This principle itself is not too wrong, but it is often encountered that recurrence or metastasis is found within a short period of time after gastric cancer surgery, in fact, metastasis is present before surgery, only that it is not detected. In the early years, the proportion of gastric cancer patients with simple surgical exploration was not low, but the surgery just opened the abdominal cavity to look at it and found that there were metastases in the abdominal cavity or could not be removed, making the patients endure the pain of anesthesia and surgery. In fact, the current medical level can almost completely avoid the above scenario. What does it depend on? It is the pre-surgical examination. As the importance of comprehensive treatment of gastric cancer has become apparent and accepted, staging examination has become a necessary step before treatment. The main purposes of staging examination include: firstly, to determine the clinical stage and to determine the comprehensive treatment plan based on the clinical stage; secondly, to determine the possibility of surgery, the possible difficulty and the possible surgical plan, the impact on the patient’s quality of life and survival. The main ideas include: excluding distant metastases, and excluding tumors one by one according to their possible metastatic sites. In addition to excluding common metastatic sites, it is also necessary to determine the possible metastatic sites according to the patient’s symptoms. For example, if a patient with gastric cancer has recently developed unexplained headache, he or she needs to be alert to the possibility of brain metastasis. Common metastatic sites of gastric cancer include liver, lung, bone, brain, adrenal gland and so on. Generally, lung metastases are excluded through chest X-ray or CT examination, liver and adrenal metastases are excluded through abdominal CT examination, and most bone metastases need to be detected early through bone scan. In addition to determining the scope, size and relationship with surrounding organs of gastric cancer, abdominal CT and MR examinations can also detect whether there is ascites, omental nodes and other abdominal metastases. In recent years, a new examination method, PETCT, has emerged and is increasingly used in clinical practice. This technique is increasingly used and has advantages in ruling out distant metastases and early detection of lesions.PETCT technique is currently the only imaging examination that combines anatomy, cell function and metabolism without significant damage. The advantages are obvious not only in the field of oncology, but also in coronary heart disease and brain diseases. It is also valuable in the early diagnosis of gastric cancer, evaluation of treatment effect and review. There can be reduction surgery or even endoscopic surgery for early gastric cancer, based on the accurate staging of early gastric cancer. Gastroscopic ultrasound technology is a very necessary one. Ultrasound endoscopy is an advanced technology emerged in recent years, which concentrates some advantages of ultrasound and gastroscopy. It involves placing a specially designed probe into the stomach lumen through the gastroscope, and the probe at the front end has the function of ultrasound to detect the tissue and organ conditions around the stomach. In the case of gastric cancer, it is possible to see the extent of invasion and the lymph nodes around the stomach. Compared with CT and other examinations, ultrasound gastroscopy has good advantages in determining the depth of invasion and lymph node metastasis of gastric cancer, so it is a necessary examination when determining whether it is early gastric cancer.