As the largest and highest plateau in the world, ecosystems on the Tibetan Plateau (TP) imply fundamental ecological significance to the globe. Among the variety, alpine grassland ecosystem on the TP forms a critical part of the global ecosystem and its soil carbon accounts over nine tenths of ecosystem carbon. Revealing soil carbon dynamics and the underlying driving forces is vital for clarifying ecosystem carbon sequestration capacity on the TP. By selecting northern TP, the core region of the TP, this study investigates spatiotemporal dynamics of soil total carbon and the driving forces based on two phases of soil sampling data from the 2010s and the 2020s. The research findings show that soil total carbon density (STCD) in total-surface (0–30 cm) in the 2010s (8.85 ± 3.08 kg C m⁻²) significantly decreased to the 2020s (7.15 ± 2.90 kg C m⁻²), with a decreasing rate (ΔSTCD) of −0.17 ± 0.39 kg C m⁻² yr⁻¹. Moreover, in both periods, STCD exhibited a gradual increase with soil depth deepening, while ΔSTCD loss was more apparent in top-surface and mid-surface than in sub-surface. Spatially, ΔSTCD loss in alpine desert grassland was −0.41 ± 0.48 kg C m⁻² yr⁻¹, which is significantly higher than that in alpine grassland (−0.11 ± 0.31 kg C m⁻² yr⁻¹) or alpine meadow (−0.04 ± 0.28 kg C m⁻² yr⁻¹). The STCD in 2010s explained >30 % of variances in ΔSTCD among the set of covariates. Moreover, rising temperature aggravates ΔSTCD loss in alpine desert grassland, while enhanced precipitation alleviates ΔSTCD loss in alpine meadow. This study sheds light on the influences of climate and background carbon on soil total carbon loss, which can be benchmark for predicting carbon dynamics under future climate change scenarios.