Millennial scale East Asian monsoon variability is closely associated with natural hazards through long-term variability in flood and drought cycles. Here we present a new East Asian summer monsoon (EASM) rainfall reconstruction from the northwest Chinese loess plateau spanning the past 650,000 years. The magnitude of millennial monsoon variability (MMV) in EASM rainfall is strongly linked to ice volume and greenhouse gas (GHG) at the 100,000-year earth-orbital eccentricity band and to GHG and summer insolation at the 23,000-year precession band. At the precession band, times of stronger insolation and increased atmospheric GHG lead to increases in the MMV of EASM rainfall. These findings indicate increased extreme precipitation events under future warming scenarios, consistent with model results.