Abstract: Based on the studies of ecosystem productivity and by means of calormetry measurement,the characteristics of energy in the formative process of net primary productivity of 21 years Dahurian Larch plantion ecosystem was studied systematically on Moer Shan Forest Farm in the eastern part of northeast China. The results showed that (1)Caloric content of plant samples varies with species, organs, ages, distributive layers and seasons. (2) Standing crop energy accumulated in the living plant is 269.719×1010 J/ha, while that accumulated in the dead plant is 36.817×1010 J/ha, in which 84.04% is in the litter and 15.96% in the standing dead plant. (3) Net energy production of Larch forest ecosystem is 264. 346 × 109 J/ha·a, 29.49 % of which goes into the litter in the form of litterfall and the rest retains in the plant for growth. The annual energy return of Larch forest ecosystem is 88.809 × 109 J/ha, with 32.39% from decomposition and rest accumulating in the litter. The energy transformation efficiency of Dahurian Larch plantation ecosystem is 2. 299%. Compared to the other plant communitie, Dahurian Larch plantation ecosystem is an energy metobolic system with a high energy conversion efficiency.