The mechanical property of cellulose is universally considered as an important parameter, which reflects the service life of cellulosic insulation paper in the transformer. In this work, the mechanical property of hydrous amorphous cellulose has been studied using molecular dynamics. Analysis of the mechanical parameters of amorphous cellulose cells reveals that amorphous cellulose remains isotropic either in the hydrous or in the anhydrous state, but shows a weakening trend in mechanical property with the increase of water content. Both intramolecular and intermolecular hydrogen bonds in cellulose molecules decrease with increasing water content, directly leading to the decline of cellulose cohesive energy density, solubility parameters, and mechanical parameters. High water content in amorphous cellulose gives bigger interchain distance of cellulose molecules, indicating that the intermolecular interaction of cellulose molecules is weakened greatly by water.