Gastric cancer is one of the most common gastrointestinal malignant tumors, which manifests itself as niche shadow when X-ray imaging is done. It is formed by the ulcer produced in the wall of the gastrointestinal tract, which is filled with barium when the imaging is done at a certain depth. Different parts of gastric cancer have different X-ray manifestations: i. fundic cancer, a huge mass in the cardia area of the fundus with irregularity; ii. gastric body cancer, a significant stenosis in the gastric body; iii. gastric sinus cancer, an irregular niche shadow in the lumen of the small curved side of the gastric sinus. The characteristics of early gastric cancer can be classified according to the typology: type I, irregular filling defect with clear boundary; type II, slight indentation with clear boundary of lesion; type III, difficult to distinguish from progressive ulcerated gastric cancer. Progressive stage: type I bulging; type II infiltrative, with stiff stomach wall, irregular margins, narrow gastric lumen, and leathery stomach; type III ulcerative, with large and shallow semilunar niche shadow and filling defect of finger pressure marks.