The orbital drift of the Fengyun 4B (FY-4B) satellite from 133°E to 105°E in early 2024 significantly altered its viewing geometry over China, providing a unique opportunity to evaluate the impact of satellite positioning on retrieval accuracy. (1) Methods: This study systematically evaluates the performance of FY-4B downward surface shortwave radiation (DSSR) products before and after the drift. To ensure a strict and unbiased comparison, a common set of exactly 147 high-quality first-order ground stations from the China Meteorological Administration (CMA) was exclusively utilized for both the 2023 and 2024 periods. The evaluation focuses exclusively on the summer season, as its complex weather conditions provide a rigorous testbed for algorithmic stability. (2) Results: The results demonstrate a substantial improvement in product accuracy post-drift. The correlation coefficient (R) increased from 0.93 to 0.95, while the root mean square error (RMSE) decreased by 11.8% (from 111.5 to 99.58 W/m²). The mean bias error (MBE) shifted from 0.64 W/m² to 1.27 W/m². Spatially, the "East-West" accuracy disparity was notably mitigated. This improvement is fundamentally attributed to the substantial reduction in the Viewing Zenith Angle (VZA) over western China, which minimized geometric distortions and atmospheric optical path errors. While performance over homogeneous surfaces is robust, challenges persist in complex terrains due to 3D topographic effects. (3) Conclusions: The optimized viewing geometry (reduced VZA) significantly enhances the satellite-ground consistency of FY-4B. The validated high-fidelity radiative records position FY-4B as a reliable data source for solar energy resource assessment, offering strategic guidance for the orbital deployment of future geostationary constellations.

FY-4B satellite; shortwave radiation; satellite-ground consistency; land cover type; eleva-tion