Abstract Summer near‐surface vapor pressure deficit (VPD), a key measure of atmospheric dryness, has increased markedly across East Asia since 1980, yet the relative roles of external forcing and internal variability (IV) in its multidecadal changes remain unclear. Here we show that IV dominates East Asian VPD variability during 1901–2024, accounting for about 81% of the total variance and largely explaining the recent drying over northern China. We identify the Indian Ocean Basin Mode (IOBM) as a key oceanic driver of this variability. A positive IOBM phase triggers a Pacific–Japan pattern‐like teleconnection, enhances subsidence and warming over East Asia and suppresses moisture transport into northern China, thereby increasing VPD. Indian Ocean pacemaker experiments capture the main circulation and warming responses, supporting this mechanism. Together, these results provide robust evidence that tropical Indian Ocean–driven IV has played a decisive role in recent atmospheric drying over East Asia.