Abstract: Plant polysaccharides, one of the main sources of natural polysaccharides, has significant antitumor activity and are potentially exploitable in the field of food and medicine. This paper systematically summarizes the anti-tumor mechanism and structure-activity relationships of plant polysaccharides, focusing on three perspectives: Inhibition of tumor cell growth, enhancement of immune regulation, and inhibition of tumor cell invasion and metastasis. The functional-structural relationships of plant polysaccharides are further dissected based on their molecular weight, glycosidic bond types and monosaccharide composition, modified modifications and advanced structures. In this paper, the antitumor activity and structure-bioactivity relationships of plant polysaccharides are systematically summarized to provide a reference for discovering its new breakthroughs and further development.