<p>Using precipitation data from the Mount Emei station, along with the CRU and APHRODITE precipitation datasets and various reanalysis products, we examined the interdecadal change in the relationship between summer rainfall on the southeastern edge of the Tibetan Plateau (SETP) and tropical sea surface temperature (SST) in the Indo-Pacific Ocean. Our findings indicate that the negative correlation between SETP rainfall and Niño3.4 SST enhanced significantly from 1985 to 2005 (P2) compared to the earlier period from 1958 to 1978 (P1). An anomalous anticyclonic belt extending from the western North Pacific (WNP) to the northern Bay of Bengal is the primary factor contributing to above-normal summer precipitation over the SETP during both periods. The intensified correlation in P2 results from synergistic interactions between Niño3.4 and the southeastern Indian Ocean (SEIO) SST. During P2, westward-extended cold SST anomalies in the central-eastern Pacific induce a westward shift of local downdrafts, which strengthen the anomalous Walker circulation and enhance convective updrafts in the equatorial western Pacific. Meanwhile, warm SEIO SST anomalies strengthen ascending motions over the southern Maritime Continent. These dual forcings jointly generate meridional circulation, leading to pronounced WNP descending branches that suppress local convection. This suppression subsequently facilitates the development of Rossby waves, forming an anticyclonic belt from the South China Sea to the Bay of Bengal. Simultaneously, SEIO-driven circulation gives rise to downdrafts south of the Tibetan Plateau, which reinforce the Bay of Bengal anticyclone; concurrently, it triggers robust ascent over the Tibetan Plateau, directly boosting SETP rainfall.​ In contrast, weaker Niño3.4- and SEIO-linked equatorial convection fails to excite these downdrafts and anticyclonic development in P1, resulting in negligible SETP rainfall responses.</p>