Abstract: It is quite difficult to identify the various kinds of deformation in the apparent mechanical behaviour of poplar wood as loaded perpendicular to its grain. However, by means of separating the theological parameters, it was found somewhat effective in studing of the theological behaviour of poplar wood under compression perpendicular to its grain. The various kinds of deformations of the specimen under various temperature and moisture content, as well as the rheological behaviour of the specimen with water vapour passing through them were investigated. The testing condition is so designed for the better understanding of the theological behaviour of wood material in compression as it occurs in pressing process of particleboard. The viscoelasticity reveals the mechanical properties of high polymers of three dimensional network. The elastical compliance and retarded elastic compliance of the specimen increase only slightly with increasing temperature in the testing range (20—105℃) in ovendry condition, increase sharply with increasing temperature in wet condition or with water vapour passing through specimen. In the condition of room temperature, the elastic compliance and retarded elastic compliance increase definitely with increasing moisture content of specimen.