Abstract: Molecular dynamics(MD) simulation method was used to study the structure and mechanical properties of cellulose I_β, the main component of wood, in heat treatment environment. A 3×3×3 cellulose supercell model for simulation was established. The volume, density, and hydrogen bond change diagrams of 350-550 K were obtained. Changes in the microstructure of cellulose were analyzed and the mechanical properties were calculated. The results showed that the unit cell volume increased gradually with the temperature increase, from 11.99 nm³ at 350 K to 12.26 nm³ at 550 K, and the density of model was 1.581-1.617 g/cm³, which was consistent with the experimental results. The total number of hydrogen bonds decreased by 24%, and the hydrogen bonds in the molecular chain were partially broken to form new interchain hydrogen bonds. The ratio of hydrogen bonds in the chain to hydrogen bonds between chains changed from 2.1:1 to 1:1.5, which in turn affected its mechanical properties. As the temperature increased, the Young's modulus gradually decreased, and the rate of change was about 13%. Shear modulus and bulk modulus were less affected by temperature compared with Young's modulus and there were no significant changing trend.