Abstract: Abstract: Stand density is one of the main technical measures in forest management. By studying the impact of stand density on the carbon storage of Pinus sylvestris var. mongolica plantation ecosystem in sandy land, this paper explores the optimal stand density management technology of Pinus sylvestris var. mongolica plantation in sandy land, in order to provide a theoretical basis for the management of Pinus sylvestris var. mongolica plantation in sandy land, and plays an important role in promoting the precise management of Pinus sylvestris var. mongolica plantation in sandy land. Taking Pinus sylvestris var. mongolica plantations with different densities (462, 661, 1061, 1393, 1573, 1623, 2492 plants·hm-2) as the research object, the differences of carbon storage and distribution characteristics in the ecosystem (arbor layer, understory vegetation layer, soil layer) were studied. The carbon storage of Pinus sylvestris var. mongolica plantation ecosystem and its components increased gradually with the increase of stand density as follows: tree layer, ecosystem carbon storage; The carbon storage of Pinus sylvestris and the carbon storage of understory vegetation layer decreased with the increase of stand density; Soil surface carbon storage increased first and then decreased with the increase of stand density, and the stand density with the best carbon storage was 1500 plants·hm-2. The carbon storage allocation characteristics within a Pinus sylvestris plantation ecosystem on sandy land are as follows: tree layer (85.21%–94.89%) > soil layer (2.73%–11.13%) > litter layer (2.12%–4.08%) > understory vegetation layer (0.06%–0.40%). Stand density significantly influences the carbon storage and its allocation pattern in these plantations. The total ecosystem carbon storage is primarily determined by the carbon stored in the tree layer, and increasing stand density is generally beneficial for enhancing the overall ecosystem carbon stock. Currently, the contributions of other components (soil, litter, understory) to the total ecosystem carbon storage remain relatively low compared to the tree layer. While the effect of excessively high stand density on total carbon storage is not fully understood, it is recognized that overly high densities can intensify intraspecific competition among Pinus sylvestris individuals, potentially negatively impacting their growth and development. Therefore, future afforestation and forest management practices must integrate carbon sequestration objectives with the maintenance of stand health and long-term stability into a comprehensive consideration