Problem of moisture influence on load bearing capacity of corrugated plywood shell that is used as a main load bearing element in hybrid panel is considered. The core of panel consists of a set of corrugated plywood shells that are stiffened with longitudinal and shear stiffness diaphragms which are made of plywood. Both sides of panel consist of flat plywood plate. The free space between panels surfaces are filled with expanded polystyrene foam (EPS). The panel is used as a load bearing construction of wall or slab. As a result of defects and heterogeneity of the panel construction during the exploitation the moisture content of wood at local regions can change significantly. It can produce a significant reduction of load bearing capacity. The moisture content change is modeled as bound water (water content below wood fiber saturation point- FSP) diffusion in wood. Mathematically it is described by Fick`s second law (isothermal case). Data of temperature-moisture seasonality in Riga was used in the calculation. The moisture diffusion depends on initial moisture content of plywood. Stress state and deflection of panel change in time are analyzed. Rational initial moisture content that produces minimal stress and deflection increase as result of local moisture influence is proposed.