Abstract: Old-growth forest is one of the vital carbon pools of forest ecosystem.It is important to study the internal and external carbon transition in old-growth ecosystem to know the carbon budget of regional-scale forest ecosystem.Based on the data of forest inventory for planning and designing,and forest disturbance statistics data,the amount of carbon turnover and off-site transport of spruce forest was estimated in Diqing Tibetan Autonomous Prefecture with the utility of CBM-CFS3 model.The results showed that annual internal carbon transition of old-growth spruce forest averaged 158.66Gg·a-1 which including 87.48Gg·a-1 from the transition of above-ground biomass to dead organic matter (DOM) pools and 71.18Gg·a-1 from the transition of below-ground to DOM pools.The annual total external carbon transition averaged 176.22Gg·a-1,which including 33.09Gg·a-1 from harvest wood,2.62Gg·a-1 from product combustion emission and 140.51Gg·a-1 from decomposition of dead organic matter.NPP,NEP and NBP averaged 145.45,4.95 and -30.77Gg·a-1,respectively.Old-growth spruce forest acted as a carbon sink during the whole simulation,whereas it converted to a slight carbon source after 2007.Harvesting is one of the major factors which drive the carbon transition of old-growth spruce forest in Diqing.Through enhancing the internal carbon turnover,removing the wood product and stimulating the heterotrophic respiration and combustion emission,consecutive harvesting disturbance increases the risk of changing old-growth spruce forest into a carbon source.