The carbon density and production were measured using both forest inventory and allometry approaches in the declining valley sprucefir  forest in Xiaoxing’an Mountains. Results showed that the total carbon density of the forest was 268.14 t C·hm^-2 in 2011, and carbon densities of the vegetation, detritus and soil were 74.25, 16.86 and 177.03 t C·hm^-2, respectively. From 2006 to 2011, tree layer carbon density decreased from 80.86 t C·hm^-2 to 71.73 t C·hm^-2. The average decrease proportions per year of carbon density were 0.5%, 1.2%, 2.7% and 3.7% for Abies nephrolepis, Betula platyphylla, Picea spp., and Larix gmelinii, respectively. However, carbon densities were increased by 2.9%, 3.9% and 7.2% per year for Alnus sibirica, Pinus koraiensis and Acer ukurunduense, respectively. Net primary production (NPP) of the forest was 4.69 t C·hm^-2·a^-1. The ratio of belowground NPP to aboveground NPP was 0.56. Litterfall accounted for the largest proportion of the NPP of forest with a value of 34.5%. As the two most important carbon output approaches of forest ecosystems, the fluxes of heterotrophic respiration and coarse woody debris decomposition were 293.67 and 119.29 g C·m^-2·a^-1, respectively. Net ecosystem production (NEP) of the forest was 55.90 g C·m^-2·a^-1. The results indicated that the  valley sprucefir forest in the declining state still had a certain carbon sink capacity.