Heat treatment is an environmentally friendly method which can improve the decay resistance and dimensional stability of wood. In this study, in order to investigate the effects of thermo-vacuum treatment on dynamic water vapour sorption and chemical properties of larch wood, wood samples were treated at 200 ℃ in a vacuum oven for different durations. The changes of wood hygroscopicity before and after heat treatment were characterized by dynamic water vapour sorption. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopic (XPS) and X-ray diffraction were used to characterize the changes in the chemical composition. The results showed that the equilibrium moisture content of wood decreased as the treatment time increased. FTIR and XPS found that the chemical composition of wood such as cellulose and hemicellulose degraded after heat treatment and the crosslinking condensation reaction of lignin occurred resulting in the decrease of the content of hygroscopic group. During heat treatment, the contents of carbon and oxygen changed and O/C ratio decreased. Besides, changes were also identified from the detailed C(1s) spectra. The C1 content of heat treated wood increased, and the C2 and C3 contents decreased. These chemical changes reduced the hygroscopicity of the heat treated wood. The relative crystallinity of wood increased with the increase of heat treatment time. The increase of the crystallinity decreased the number of water-absorbing groups on the cellulose chain, which decreased the hygroscopicity of wood.