Abstract: The tobacco leaf polysaccharide was carboxymethylated, and added to the cut tobacco to carry out physical water retention performance measurement. At the same time, pyrolysis products of tobacco leaf polysaccharide and carboxymethyl tobacco leaf polysaccharide was carried out by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The results of water retention performance were as follows:under low humidity conditions, the moisture content of four samples of cut tobacco was carboxymethyl tobacco leaf polysaccharide > glycerol > tobacco leaf polysaccharide > blank. Under high humidity conditions, the moisture content of cut tobacco was glycerol > blank > tobacco leaf polysaccharide > carboxymethyl tobacco leaf polysaccharide. Carboxymethyl tobacco leaf polysaccharide could slow the change of cut tobacco moisture content under high humidity or low humidity conditions. The results of Py-GC/MS showed that there were 55 pyrolysis products in tobacco leaf polysaccharides and 43 pyrolysis products in carboxymethyl tobacco leaves. Both polysaccharides could produce aroma substances such as furfural and pyridine. Compared with the pyrolysis products of tobacco leaf polysaccharide, the production of carcinogenic components such as toluene and phenol from carboxymethyl tobacco leaf polysaccharides was relatively few. Carboxymethyl tobacco leaf polysaccharide had a better water holding effect, and after pyrolysis, it could produce aroma substances which contributed to cigarette smoke.