Natural polysaccharides as sustainable polymers are rich sources with good biological safety and various biological functions, which are important research topics in the fields of food and medicine. However, their widespread medical application is hindered due to the technical difficulties in the extraction/purification and chain structure characterization of polysaccharides, as well as due to the lack of thorough understanding of the macromolecular chain conformation and the mechanism of bioaction for these polysaccharides. To provide a relatively comprehensive reference for relevant researchers, we mainly introduce several natural polysaccharides with different chain conformations including random coil, hyperbranched sphere, and triple helix in solution, as well as summarize their extraction and purification processes, characterization of chemical structure and chain conformation, anti-tumor activities and potential mechanisms.