Abstract: It is suggested that the phonon is the carrier of the transmission of thermal energy in wood in this paper. The theoretical expression of the thermal conductivity of wood in the radial direction is developed on the basic principles of the physical mecha nics. Then, the thermal conductivity of 18 species of trees can be calculated by the formula with the maximum relative error 13.7%, the average relative error 5.3%. Compared with the experimental value in the same condition, the calculation result is satisfactory.

Key words: wood, radial direction, thermal conductivity