Abstract: In order to explore the forest composition and structure,tree carbon stock and allocation,researches were conducted on Larix kaempferi plantation,Phellodendron amurense plantation,Pinus armandii plantation,and natural second forests dominated by Juglans cathayensis,and Quercus variabilis and Fagus spp.,which were located in the middle mountain of Laohegou Nature Reserve within the Pingwu County,northwestern Sichuan.The results showed that the composition and structure varied largely in different forests.The carbon stock of 5 kinds of forests varied from 96.88±2.20 MgC per hectare to 282.61±7.94 MgC per hectare,the most of the carbon was stocked in the aboveground part of forests.The carbon stock in the different tissues in different forests or plantations varied significantly.For the in situ carbon stock in the middle mountain of Laohegou Nature Reserve,the first was the natural forest dominated by Juglans cathayensis,and the second was the mixed forest dominated by Quercus variabilis and Fagus spp.