The trophic structure and the function of a small pond ecosystem under the tree stand were studied in term of energy flow. About 28% of total solar radiation was intercepted by the tree canopy over the pond. Primary producers converted 1.1%(3,382 ㎉·m^-2·y^-1) of solar radiation (320,000 ㎉·m^-2·y^-1) into gross primary production. The amount of energy available to the pond sanil was 1,683 ㎉·m^-2·y^-1 of the net production by primary producers and 1,033 ㎉·m^-2·y^-1 of the litter fallen into the pond. The amount of gross secondary production by the pond snail was 245 ㎉·m^-2·y^-1. Judging from these, supply of both net primary production and the litter was indispensable for the maintenance of the pond ecosystem. The total amount of energy as gross primary production plus litter was 4,415 ㎉·m^-2·y^-1(100%). Since the total respiration loss was calculated to be 1,917 ㎉·m^-2·y^-1(43.4&), the rate of energy accumulation in the pond estimated to 56.6%.