Thermodynamic moisture retention properties of microbial polysaccharides and seaweed polysaccharides were investigated as compared with water and propylene glycol. Then three common dynamic models of tobacco were selected to fit the hygroscopic and desorption processes of tobacco. The results showed that the moisture retention of Laminaria japonica polysaccharides and Spirulina platensis polysaccharides was significantly better than that of propylene glycol, and page model was the best. Considering the thermodynamic and kinetic factors according to the moisturizing index, Laminaria japonica, Spirulina platensis and Hericium erinaceus polysaccharides were considered to have better moisturizing effect. Low field nuclear magnetic results showed that the addition of aforementioned three polysaccharides increased the chemically bound water content in tobacco as compared with the addition of water and propylene glycol, thus the moisture in the tobacco is less likely to be lost.