Objectives Natural protected areas are the key supporting regions to implement carbon neutralization action in China. Accurate estimations of carbon storage and carbon sequestration potential of forest vegetation are important measures to address climate change and coordinate the coordinated and comprehensive regional eco-economy and social development.

Methods The research area for the study was Qilian Mountain National Nature Reserve in Gansu Province. The data set for the study was derived from the forest resource survey of the second category. The tree species (group) and age group were the basis for evaluating the carbon storage and density and potential of forest vegetation in the nature reserves. The volume-source biomass method and the space-time substitution method were used to conduct this evaluation.

Results (1) The total carbon storage of forest vegetation in Qilian Mountain National Nature Reserve in Gansu Province was 1.41×10⁷ Mg, and the average carbon density was 21.09 Mg/hm². The proportion of carbon storage in arbor forests accounted for 73.62%, and the average carbon density was 6.45 times that of shrub wood and 1.15 times that of open forests. (2) The carbon storage and carbon density of forest vegetation were greatly various in different regions. The regions of Longchang River Reserve (1.50×10⁶ Mg) and Longshou Mountain Reserve (1.91×10⁴ Mg) had the highest and lowest carbon storage, and the areas with the highest and lowest carbon densities were Changling Mountain Reserve (39.7 Mg/hm²) and Dongdahe Reserve (12.68 Mg/hm²), respectively. The establishment of a national park system and a rational and orderly increase in afforestation tasks have a positive effect on improving the carbon sequestration capacity of forest vegetation. (3) The carbon storage of Picea crassifolia Kom. accounted for 66.98% of the total carbon storage in the forest area, and the average carbon density of Betula albo-sinensis Burk, pure forest and coniferous and broad-leaved mixed forest of Picea crassifolia Kom. was greater than 40 Mg/hm², which was higher than that of other forest types. (4) The forest species with the greatest carbon storage and average carbon density are nature conservation forests and other shelter forests, respectively, and the forest age group with the largest carbon storage and average carbon density are mature forest and near-mature forest. (5) The total carbon sequestration potential of the forest area was 1.00×10⁷ Mg, and the main contribution was the afforestation projects of other barren mountains and beaches suitable for afforestation.

Conclusions The research results can provide valuable insights that can inform international climate negotiations and research endeavors concerning the Earth’s carbon cycle. They also established a foundation for evaluating forest carbon sources and sinks, as well as for assessing the storage of carbon within forests. Furthermore, the study provided a technical support for forest management level evaluation and management measures tracking guidance.