Summer monsoon precipitation over the Tibetan Plateau (TP) has significant impacts on the ecology, economy, and Asian climate, but has exhibited anomalous spatial distribution since the early twenty-first century. To explore its distribution and attribution, this study investigated the northernmost boundary of the summer monsoon over the TP (TPSM) and the related precipitation. The TPSM and related precipitation extended poleward in the post-2000 period in response to the rising Arabian Sea surface temperature (ARB_SST) in the late spring and early summer. A warming Arabian Sea leads to the westward movement of the Indian summer monsoon (ISM) circulation and moisture convergence with a higher moisture layer, which exerts a midlatitude wave train that exhibits a dipole mode (a west cyclone and an east anticyclone) over the TP. Consequently, the west trough and southerly are strengthened, which is conducive to transporting more poleward moisture mass from the moisture layer over the ISM zone through the midwestern TP. Furthermore, it contributes to the poleward TPSM and precipitation in the northern TP by coupling with the dipole mode. These findings help explain the wetting of the Asian dryland and its effects on the Northern Hemispheric climate.