Erosion in the buffer layer of high-voltage crosslinked polyethylene (XLPE) cable has become a significant concern, severely threatening the stability of power grids. This work statistically reviewed recent cases of buffer layer erosion and constructed a simulation platform to examine the impact of pressure and humidity on erosion. The results show that in humid conditions, as the pressure rises, the erosion voltage of buffer layer drops from 36 V to 24 V, and the current changes from 1340 mA to 879 mA. Conversely, in dry conditions, the voltage decreases from 24 V to 15 V, while the current increases from 155 mA to 952 mA with rising pressure. SEM and energy dispersive spectrometry (EDS) of the eroded products identify the formation of white powder, primarily due to the precipitation of water-blocking agents from the buffer layer. Finite element analysis elucidates the erosion mechanism, highlighting the role of the mass of cable under gravity and ambient humidity fluctuations in causing erosion. The outcomes of this study could offer theoretical foundation and experimental evidence for developing erosion protection strategies of XLPE cable buffer layers.