Australian monsoon significantly modulates hydroclimate conditions over the densely populated Indo-Pacific region. However, its changes and influencing factors on millennial timescale remain mysterious by so far owing to scarce of high-resolution records. This study presents millennial-scale records of the Australian summer monsoon (AuSM) and winter monsoon (AuWM) for the past ~22 kyr, based on clay mineral assemblages and mean grain size of sediments from Core SO18567 retrieved offshore northwest Australia. Comparison of the new records with published records, together with TraCE-21 ka and CLIMBER-X modelling results, indicates the strengthened AuSM during the Heinrich Stadial 1 (HS1), which could be ascribed to southward migration of the Intertropical Convergence Zone (ITCZ) induced by collapse of the Atlantic Meridional Overturning Circulation. It also indicates gradual strengthening of the AuSM in the Holocene, which could be due to increased austral summer insolation. By contrast, the dramatic weakening of AuWM is observed during the HS1, likely due to the joint influence of reduced atmospheric pressure gradient between Asian and Australian continents caused by insolation contrast between two hemispheres and southward displacement of the ITCZ, whereas gradual weakening of the AuWM during the Holocene could be caused by the former.