Stomach cancer is a common disease in China, and due to the large population base in China, about half of the new cases of stomach cancer worldwide appear in China every year. Therefore, the prevention and treatment of gastric cancer is a topic that we cannot stop talking about, and the mentality of talking about cancer in the past must be abandoned. The treatment of any disease starts from the diagnosis, and successful treatment is based on the correct diagnosis. Stomach cancer is no exception. Generally speaking, the diagnosis of gastric cancer is divided into two parts, “qualitative” and “quantitative”. The so-called “qualitative” diagnosis refers to the clarification of the benign and malignant nature of the lesion. Whether it is a benign inflammatory polyp or adenoma, or an adenocarcinoma. The gold standard for qualitative diagnosis is the pathological findings, that is, the suspicious lesions taken by gastroscopic biopsy, which are processed and analyzed by the pathologist. It is worth mentioning that in some difficult cases, a single biopsy may not be able to retrieve the lesion, or the tissue retrieved may not be sufficient for the diagnosis, and the doctor will arrange for another biopsy until the diagnosis is clear. Very rarely, empirical treatment may be used to buy time for treatment without obtaining a pathological diagnosis. For example, a gastroscopic biopsy report indicating “moderately differentiated adenocarcinoma” would indicate that the lesion is characterized as malignant. The “quantitative” diagnosis is to determine the extent of the disease, or early, intermediate and late stages, if the diagnosis of malignancy is confirmed. Different treatment strategies are different for different stages, thus the stage diagnosis is very important. The quantitative diagnosis of gastric cancer is mainly based on the results of the following auxiliary examinations: gastroscopy and/or ultrasound gastroscopy, abdominopelvic enhanced CT, plain CT of the chest, and PET-CT if necessary. gastroscopy and ultrasound gastroscopy can clarify the location of the lesion, determine the depth of invasion of the lesion in the stomach wall, and initially determine the early and late stage of the lesion. CT of the abdominopelvic cavity, on the other hand, can clarify the relationship between the lesion and surrounding organs such as the pancreas, liver, diaphragm, abdominal aorta, etc., and determine the metastasis of abdominal lymph nodes and the presence of liver and peritoneal metastases. Chest CT can clarify whether there is lung metastasis. For progressive gastric cancer, when distant metastasis is suspected, additional PET-CT is needed to clarify the diagnosis. With the combination of both qualitative and quantitative diagnosis, doctors can classify patients into different stages and take appropriate treatment. The symptoms and signs that we usually pay more attention to are actually of limited significance to the diagnosis of the disease, because in clinical practice, about half of the gastric cancer patients do not have obvious symptoms, which is the insidious nature of the onset of gastric cancer. When symptoms and signs such as weight loss, loss of appetite, swollen supraclavicular lymph nodes, black stool or even vomiting blood appear, most of them lose the chance of radical treatment. I would like to take this opportunity to sincerely remind all patients and readers to pay attention to their health, pay attention to regular medical checkups, early detection, early diagnosis and early treatment of the disease. An endoscopist once said, “Finding an early cancer saves a family.” This is a true statement.