The substantial soil carbon pool in tundra ecosystems magnifies the importance of even minor alterations, as these can significantly influence atmospheric CO₂ levels and are pivotal in managing the global carbon balance. Herbaceous plants beneath Betula ermanii in Changbai Mountain are encroaching on the tundra, causing considerable shifts in the tundra's vegetation. To explore the impact of exogenous carbon inputs on soil organic carbon mineralization and associated components within the tundra, a 120 day lab incubation experiment was undertaken..This study selected the indigenous shrub species Rhododendron aureum and the invasive herbaceous species Deyeuxia angustifolia. Surface soil samples (0-15 cm depth) were obtained from plots dominated by Rhododendron aureum, and six litter treatments were implemented to mimic varying degrees of herbaceous encroachment. The findings revealed that: (1) In contrast to shrub litter inputs, a higher proportion of herbaceous plant inputs substantially boosted the rate of soil organic carbon mineralization, the cumulative mineralization of soil organic carbon, and the positive priming effect, especially in the incubation's initial stages. And all measurement parameters were higher with higher-quality mixed litter input than with higher-quality single herbaceous plant litter input. (2) As the proportion of herbaceous plant input increased relative to shrub litter input, the total organic carbon quantity and the proportion of heavy fraction organic carbon in the soil organic carbon pool decreased, while the proportions of microbial biomass carbon, dissolved organic carbon, easily oxidated carbon, and light fraction organic carbon increased, and the content of readily available nutrients also increased. (3) Correlation analysis, along with single first-order single exponential model and first-order double exponential decay model studies, indicated that high-quality exogenous carbon inputs promoted soil organic carbon mineralization, while low-quality exogenous carbon inputs favored the stabilization of soil organic carbon. In summary, As the invasion of herbaceous plants escalates, the soil organic carbon becomes increasingly unstable, Conversely, when herbaceous plants entirely replace shrubs in the future, the soil organic carbon in the tundra may become relatively stable.