<p>The Antarctic ice sheet stores approximately 70% of the world’s freshwater resources, and its mass balance is critical to global sea-level changes. Satellite radar altimetry is a key technology for monitoring ice sheet changes, but its accuracy is significantly constrained by the penetration depth of the signal into the snowpack. Penetration depth depends on the physical properties of the surface snow layer, which are modulated by large-scale climate oscillations. This study integrates ICESat-2 laser and CryoSat-2 radar altimetry data to construct a high-resolution (27.5 km) monthly time series product of penetration depth over the Antarctic ice sheet from October 2018 to December 2022. It systematically reveals the spatiotemporal variations of penetration depth and explores the associated mechanisms with the El Niño-Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). The results show significant spatial heterogeneity in penetration depth, with the highest average value in the Antarctic Peninsula (2.66 m) and strong seasonal fluctuations, while the East Antarctic ice sheet is the most stable (1.15 m). ENSO and SAM significantly modulate penetration depth by influencing snow temperature, precipitation, and melt processes. This study enhances the understanding of penetration depth, quantifies the impact of climate modes on microwave signal propagation, and provides key scientific support for developing subsequent penetration depth correction models and improving the accuracy of ice sheet mass balance monitoring.</p>