Numerous tree-ring and historical records indicate a megadrought in the Loess Plateau (LP) of northern China during 1928-29, yet its dynamical causes remain unclear. This study reconstructs LP summer precipitation from 1901 to 2000 using multiple paleoclimate proxies to assess precipitation and reanalysis data sets. The results show that 1928 and 1929 were the driest and second-driest years of the twentieth century, with precipitation deficits of 2.96 and 2.25 standard deviations and return periods of 160 and 40 years, respectively. Existing precipitation and reanalysis data sets failed to capture this event due to a lack of reliable observations in the Asian and Pacific regions. More reliable European meteorological data suggest that this event was primarily driven by extreme cold over northern Europe, which triggered eastward-propagating Rossby waves, inducing high pressure over Mongolia and suppressing ascent over the LP.