<p>The Qilian Mountains, located at the frontal margin of the northeastern Tibetan Plateau, are characterized by complex surface and deep-seated deformation. Investigating its lithospheric structures and related geodynamic processes is crucial for further understanding northeastward growth of the Tibetan Plateau. In this study, we integrate the high-precision gravity and GNSS data with gravity anomaly models to derive a high-resolution regional gravity anomaly field in the eastern Qilian Mountains. Based on the observed Bouguer gravity anomalies, we invert the crustal density structure, and further estimate the regional effective elastic thickness (<i>Te</i>) and loading ratios(<i>F</i>) using the free-air gravity anomalies and high-resolution topographic. Our results reveal pronounced compressional folding in the crust beneath the North Qilian and Longshoushan fault zones. In particular, the Moho beneath the Longshoushan Fault dips southward, marking this structure as the leading edge of the northeastern Tibetan Plateau’s outward expansion. The inferred Te is ~ 9.8 km, indicating a relatively weak lithosphere prone to deformation. The estimated loading ratios are as follows: surface loading (F₁ = 0.18), intra-crustal loading (F₂ = 0.02), and upper mantle loading (F = 0.80), suggesting that tectonic deformation is predominantly driven by loads from the Moho. Integrating current geodetic and geophysical evidence, we propose a geodynamic model in which the passive southward underthrusting of the North China Craton lithosphere, coupled with large-scale mantle convection, facilitates mantle upwelling. We suggest that this deep-seated process, acting in concert with lithospheric block compression and upper-crustal shortening, drives the rapid uplift of the eastern Qilian region.</p>