Abstract: Using gird system and layer methods, the characteristics of canopy structure and the patterns of light distribution in the 8yearold trees in four different high densities(4 m×3 m,3 m×25 m,3 m×2 m,3 m×15 m) orchards of chestnut(Castanea mollissima) were studied in Xin Yi county, Jiangsu province. The results showed that the diameter of canopy reduced, the layer of green leave raised,the thickness of canopy decreased and the volume of canopy reduced with the density increased; The light distribution in the different layers of the canopy varied with the changes of the natural sunlight. The mean daily light transmissivity and the daily changes of the light intensity were reduced from the external to the internal part of the canopy. The light distribution in the canopy and the efficience of its utilization were obviously affected by the structure of canopy and the leaf area index(LAI). The best density that has high efficience light usage should be maintained with 834～1334 trees.gha-1, with the thickness of canopy more than 2.0 m and an effective leaf area index of appoximately 5～6.