Ground ice content plays a key role in controlling permafrost stability in the source region of the Yellow River, yet its quantitative characterization is limited by strong subsurface heterogeneity and scarce direct observations. This study integrated ground-penetrating radar (GPR) and opposing coils transient electromagnetic (OCTEM) data within a joint inversion framework based on full-waveform inversion (FWI) to estimate volumetric ice content (VIC) at four high-altitude permafrost sites. The results showed strong lateral and vertical variability in VIC, with distinct VIC magnitudes and depth-dependent patterns among sites. Shallow VIC derived from radar-based dielectric properties provided physical constraints for estimating deeper VIC through a calibrated relationship between relative permittivity and apparent resistivity. Ice-rich and ice-poor zones were spatially consistent with apparent resistivity sections and forward-modeled electromagnetic responses, supporting the reliability of the integrated approach. Estimated VIC at depths from 2 to 10 m was relatively low at Huashixia, at approximately 8–15 %, but generally exceeded 20 % at Hela, Shuangchagou, and Maduo. This study demonstrated the effectiveness of a physically constrained electromagnetic strategy for quantifying VIC in alpine permafrost.