Using the observation and reanalysis data in 1900-2014, this study shows that impacts of Atlantic Zonal Mode (AZM) on the interannual variations of Australian autumn precipitation can be modulated by Interdecadal Pacific Oscillation (IPO). When the IPO is in the positive phase, AZM decreases the autumn precipitation in central Australia. Whereas, when the IPO is in the negative phase, AZM increases the autumn precipitation in central and southern Australia. This is because during the IPO positive phase, the anomalous warming and ascending motion in the tropical Atlantic related to the AZM can induce anomalous descending motion over the tropical eastern Pacific, leading to anomalous upward motion around the Maritime continent. The anomalous upward motion adjusts the local Hadley circulation and causes anomalous subsidence in central Australia, This, together with the anomalous anticyclone in the lower troposphere whose southeasterly anomalies along the northwestern frame hindering the transport of warm and humid water vapor from the tropical Indian Ocean, results in precipitation deficit in central Australia. In contrast, during the IPO negative phase, due to the different basic state and stronger AZM amplitude when compared with those during the IPO positive phase, the Rossby wave in the mid-high latitudes of the southern hemisphere caused by the AZM induces a barotropic cyclone in Australia. The anomalous cyclone not only trigger the anomalous ascending motion, but also help transport more warm moisture from the tropical Indian Ocean to central and southern Australia by the anomalous northwesterlies along the northwestern frame, leading to surplus precipitation in this region. Hence, the IPO modulates the AZM-Australian precipitation relationship by changing the basic state and the AZM amplitude.