Abstract: Based on long-term observational and reanalysis data, this study focuses on the decadal variation in the correlation between the Aleutian low (AL) and the Icelandic low (IL) during boreal winter. The results show a clear seesaw pattern in sea level pressure between the North Pacific and North Atlantic due to a negative correlation between the AL and the IL (AIS). In addition, the AIS is significant from 1935-1949 and after 1980 while it is not so significant in other periods, i.e., there exists a decadal variation in the AIS. Results also indicate that the phase transition of the Pacific decadal oscillation (PDO) during the late 1970s played a major role in the decadal shift of the AIS in the 1980s. The phase transition of the PDO from a negative to a positive phase leads to enhanced sea surface temperature (SST) over the global oceans and a reduced SST in North Pacific. In the meantime, the two lows are also deepened with a strengthened westerly on the south flanks of the lows. As a result, a negative correlation between the AL and the IL tends to become significant through the Rossby wave dispersive process. The decadal shift in the mid-1930s was much the same but with weaker intensity. We also noted that the interannual variability of the lows is influenced by the decadal climate background. Driven by the observed SST and sea ice, the IAP AGCM4 generally simulates the observed decadal shift of the AIS and related mechanisms although there are some biases in the model.