Grassland degradation is a major environmental issue on the Qinghai–Xizang Plateau (QXP), threatening ecosystem function and carbon storage. Soil organic carbon (SOC) turnover time (τ) – the average residence time of carbon in soil – reflects how quickly soil carbon cycles and is thus a key metric of soil stability. We used extensive field data from alpine grasslands across the QXP to estimate τ and analyze its environmental controls. Our results show that τ varies widely (on the order of decades to centuries) across the plateau. Slower turnover (longer τ) occurred in cooler, wetter sites with higher soil fertility and plant cover, whereas warmer, drier, and heavily grazed areas exhibited faster turnover (shorter τ), indicating destabilized carbon pools. These patterns align with known relationships of τ to climate and soil properties and highlight the impact of degradation (e.g. overgrazing) on carbon dynamics. We propose that SOC turnover time can serve as a diagnostic indicator of grassland degradation or recovery. In practice, mapping τ alongside SOC stocks would improve land degradation assessments and help target restoration (e.g. grazing exclusion, revegetation) where it can most effectively rebuild soil carbon and resilience.