Alpine meadows constitute approximately 23% of the Qinghai-Tibetan Plateau surface and are vital to ecosystem services and human well-being. Under the context of unprecedented climate warming and heavy grazing practices, alpine grasslands have been undergoing serious and extensive degradation for the past decades. Grassland degradation substantially weakened soil nutrients status and ecological carrying capacity of alpine meadows, but their spatial driving magnitudes and environmental controls remain unclear in the Three Rivers Source. From July to August in 2020, based on 60 paired soil samples of native and degraded alpine meadows in the Sanjiangyuan National Park, the spatial response of topsoil (0-30 cm) organic carbon content (SOC), total nitrogen content (TN), and total phosphorus content (TP) to grassland degradation was quantified, as well as the underlying environmental controls. The contents of SOC and TN in native alpine meadows were (2.45±2.05)% (Mean±Standard deviation, the same below) and (0.25±0.20)%, respectively. The results of the paired-samples t-test showed that the content of SOC and TN in degraded alpine meadows were significantly (P<0.001) decreased by 44.0% and 35.6%, compared to native alpine meadows. The degradation induced-loss in topsoil density of SOC and TN was 2.23 kg/m² and 0.16 kg/m², respectively, given that marginally significant (P=0.06) difference between bulk density in native (0.93 g/cm³) and degraded alpine meadows (1.12 g/cm³). The content of TP exhibited no significant (P=0.22) response to grassland degradation, because soil phosphor comes mainly from rock weathering, which was strongly affected by soil parent materials. The C:N:P of native and degraded alpine meadows averaged 59.6:6.2:1.0 and 35.6:4.2:1.0, respectively. And it was remarkably reduced by 28.3% due to grassland degradation, which might alleviate the nutrient limitations on plant growth. The difference of soil nutrients and stoichiometry between native and degraded alpine meadows was used as an indicator for the spatial effects of grassland degradation. And the general linear model analysis revealed that the spatial magnitudes of grassland degradation on SOC, TN, and soil stoichiometry were significantly related to latitude and elevation (P<0.01), rather than longitude and soil depth. This finding suggested that the response to degradation could be much stronger in alpine meadows of lower latitude and higher elevation. Therefore, grassland degradation caused serious losses of topsoil carbon and nitrogen and decreased soil stoichiometry of alpine meadows in the Sanjiangyuan National Park. These results can provide a theoretical basis for the rehabilitation and management of the soil nutrient function of the degraded alpine meadows in the Sanjiangyuan National Park.