In this study, physical mechanism of the impacts of the tropical Atlantic sea surface temperature (SST) on decadal change of the summer North Atlantic Oscillation (SNAO) was explored using an atmospheric general circulation model (AGCM) developed at the International Centre for Theoretical Physics (ICTP). The simulation results indicate that the decadal warming of the SST over the tropical Atlantic after the late 1970s could have significantly enhanced the convection over the region. This enhanced convection would have strengthened the local meridional circulation over the Eastern Atlantic-North Africa-Western Europe region, exciting a meridional teleconnection. This teleconnection might have brought the signal of the tropical Atlantic SST to the Extratropics, consequently activating the variability of the eastern part of the SNAO southern center, which led to an eastward shift of the SNAO southern center around the late 1970s. Such physical processes are highly consistent with the previous observations.