[Objective] The effects and mechanisms of soil carbon and nitrogen sequestration during vegetation restoration in desertification reversal was revealed in order to provide a scientific basis for evaluating the restoration effects of sand fixation afforestation on desertified soil quality. [Methods] Sand fixation forests of shrubs and trees in the Mu Us sandy land of Yulin City， Shaanxi Province， including changing sandy land， semi-fixed sandy land and those restored for 20—50 years were selected. Using the centrifugal group method， the characteristics of content evolution， density growth rate and contribution ratio of carbon and nitrogen in the soil and the combined state of sand， silt， and clay mineral particles in the 0—10 cm and 10—20 cm soil layers were explored. [Results] With prolonged restoration， sand-fixing forests substantially enhanced the densities of total organic carbon （TOC）， total nitrogen （TN）， and mineral particle-bound carbon/nitrogen， exhibiting linearly increasing trends. Sand fraction showed the highest carbon accumulation rate 〔0.14 Mg/（hm² · a）〕， followed by silt， whereas clay exhibited the lowest rate. After 50 years of restoration， arbor forests displayed 26.9% and 18.5% higher TOC and TN contents， respectively， than shrublands. In surface soils （0—10 cm）， the carbon content in sand， silt， and clay particles increased by 13.75， 11.37， and 5.24 times in shrublands relative to that in mobile dunes， respectively， reaching 13.73， 24.78， and 5.82 times increments in arbor forests. The surface layers of arboreal forests demonstrated significantly stronger carbon and nitrogen sequestration capacity in sand and silt particles than those of shrublands， whereas no significant differences were observed in clay particles and subsurface layers. Although sand particles contributed 42.36%—48.70% of total carbon-nitrogen increments， the combined silt and clay fractions （representing only 8.1% of total soil mass） accounted for 56.12% of organic carbon and 57.13% of TN sequestration， showing the characteristics of ‘low quantity and high efficiency’. The soil C/N ratios exhibited a unimodal pattern with the restoration chronology peaking in 20—30 years. Silt particles maintained the highest C/N ratios （26.6—39.9）， contrasting with the lowest values in clay fractions （10.7—18.4）， indicating substantial compositional differences in mineral-associated organic matter. [Conclusion] These findings highlight the critical role of vegetation restoration in enhancing soil carbon and nitrogen sequestration via accelerated sand particle accumulation and effective silt-clay adsorption mechanisms in desertification-controlled ecosystems.