One of the malignant tumors with a high occurrence rate worldwide is gastric carcinoma, which is an epithelial malignant tumor emerging from the stomach. Natural product polysaccharides are a kind of natural macromolecular polymers, which have the functions of regulating immunity, anti-oxidation, anti-fatigue, hypoglycemia, etc. Natural polysaccharides have remarkable effectiveness in preventing the onset, according to studies, and development of gastric cancer at both cellular and animal levels. This paper summarizes the inhibitory mechanisms and therapeutic significance of plant polysaccharides, fungi polysaccharides, and algal polysaccharides in natural product polysaccharides on the occurrence and development of gastric cancer in recent years, providing a theoretical basis for the research, development, and medicinal value of polysaccharides.