Larix gmelini forest is the predominant timber source in China. Chronic dependence on this species for lumber has significantly modified this forest type. Larix gmelini forest has been damaged. Age structures have changed; areas of mature and over-mature virgin forest have declined.Most of the remaining forest type is comprised of secondary young and middle-age forest. Therefore, it is important to research biomass and carbon pool of young and middle-age forest. There is the close relationship between forest biomass and fixed carbon of forest ecosystems. The amount of biomass and carbon storage directly affect functions of forest ecosystems, so biomass and carbon storage have been the focus of ecological researches in different scale. In researching the young and middle age forest Larix gmelini of Da Xing′an mountains Inner Mongolia, we estimate BEF (Biomass Expansion Factor), biomass, carbon storage, carbon density and carbon pool function of Larix gmelini′s using the standard Sample-plot survey data combined with Chinese Continuous Forest Inventory data. Through measurement data and model analysis, basic conclusions are as follows: BEF moves between 0.4557 and 0.6988, the average is 0.5332. The partition ratio of trunks, bark, branches and leaves′ biomass is 68.74: 14.86∶10.54∶5.86. The relationship between biomass and stock volume of trunks, bark, branches, and leaves is fitted to estimate the correlative model of biomass and stock volume of multiple components: Trunks: y=0.4683x-11.291; Bark: y=0.0472x+3.5674; Branches: y=0.0415x+1.6787; Leaves: y=0.0197x+1.3405, which are fairly linear. The above-ground biomass also increases as volume increases and the linear equation they follow is: B = 0.5767V - 4.7042. According to the latest CFI data, total biomass is estimated as 9.49×10⁷t by the volume-biomass method. According to 0.5097 carbon content, total carbon storage of Larix gmelini′s young and middle-age forest is 4.84×10⁷t, and carbon density is 19.616t/hm². Comparing two period data, carbon storage of forest stand and carbon density for 5 years increase by 0.89×10⁷t and 0.404t/hm² respectively, demonstrating that young and middle age forest of Larix gmelini has certain carbon sink functions. Although recently Larix gmelini of Da Xing′an mountains shows obvious carbon pool functions, overall capacity of fixing carbon is not strong and carbon density is less than Chinese average forest carbon density. By emphasising quality of intensive management and digging potential, forest ecosystem of Da Xing′an mountains will have greater influences on global carbon cycle.