Abstract: Background Clarify the carbon sequestration effect of the afforestation project in the Bashang Plateau sandy land of northern Hebei Province to provide theoretical support for regional vegetation construction. Methods This study investigated the differences in ecosystem carbon density under different afforestation species and planting patterns, focusing on Pinus sylvestris var. mongolica and Larix principis-rupprechtii plantations with two afforestation models (intercropping of trees and grasses and non-intercropping) in Yudaokou Forest Farm. Non-forested lands served as controls, categorized into three types (CKI, CKII, and CKIII) based on descending biomass levels. Results The results showed that: (1) The carbon density within plantation ecosystems is predominantly distributed in the tree layer and soil layer, while the herbaceous layer and litter layer contribute a significantly smaller proportion. (2) The carbon density of the tree layer in the non-intercropping Pinus sylvestris var. mongolica (NFGP) (36.70 t/hm2)and Larix principis-rupprechtii (NFGL) plantations(52.94 t/hm2) aged 16-18 years was significantly higher than that in the intercropping Pinus sylvestris var. mongolica (FGP) (19.41 t/hm2) and Larix principis-rupprechtii (FGL) (32.54 t/hm2) plantations (p < 0.05). The Larix principis-rupprechtii plantations under both afforestation models were significantly higher than the Pinus sylvestris var. mongolica plantations (p < 0.05). (3) The carbon density of the soil layer was in the order of CKI (127.56 t/hm2) > NFGL (110.55 t/hm2) > FGL (79.42 t/hm2) > FGP (76.85 t/hm2) > NFGP (63.07 t/hm2) > CKII (56.06 t/hm2) > CKIII (31.78 t/hm2). There was no significant difference between CKI and NFGL, but both were significantly higher than the other types (p < 0.05), and CKIII was significantly lower than the other types except CKII (p < 0.05). (4) The carbon density of the ecosystem was NFGL (178.49 t/hm²) > CKI (132.70 t/hm²) > FGL (119.48 t/hm²) > NFGP (109.88 t/hm²) > FGP (102.01 t/hm²) > CKII (59.89 t/hm²) > CKIII (34.22 t/hm²). Except for NFGL being significantly higher than the others and CKII and CKIII being significantly lower than the others (p < 0.05), there were no significant differences among the remaining types (p > 0.05). (5) Since the implementation of the "Recreate Three Saihanba Forest Farms" project, the Yudaokou area has increased its carbon storage by 1.1554 million tons of carbon through artificial afforestation. Conclusions Artificial afforestation has significantly increased the carbon storage of the sandy ecosystem in the northern part of Hebei Province, and using Larix principis-rupprechtii in a non-intercropping model can achieve higher carbon storage. Meanwhile, when the initial vegetation is good and the soil organic carbon storage is high, artificial afforestation with Pinus sylvestris var. mongolica or intercropping of the two tree species may lead to a decrease in the carbon storage of the ecosystem.