Abstract: For establishing the theory of short wave radiation through the forest canopy,in the forest four canopy cases have been considered: 1) all leaves were horizontal to light; 2) all leaves were perpendicular to light; 3) all leaves were inclined with some angle;and 4) all leaves were distributed at random. The intensity of direct lights absorbed by the forest canopy for all leaves with random distribution may be respectively expressed as following: Where I_b——intensity of direct light absorbed by forest canopy; a——reflection coefficient of the leaf; b——absorbent coefficient of the leaf; F_m——leaf area index; I_o——intensity of direct light on the forest canopy surface;l_o——intensity of direct light under forest canopy;h_o——sun elevation angle.The intensity of diffuse light may be expressed respectively as following:Where ∫I′_bdω——absorbent intensity of diffuse light from concave by forestcanopy; ω——solid angle; θ——zenith angle; I′_b—— absorbent diffuse intensity in some derection of concave; I′_o——diffuse indensity on the surface of forest canopy in some direction of concave. The above formulas agree well with the experimental data and therefore may have certain value in practice.