High temperature extremes (HTEs) have received increasing attention due to their rising impacts on human mortality, regional economies, and ecosystems. In this study, HTEs are defined as days with daily maximum temperature above the 90th percentile derived from a specific climatological period. Occurrences of summer HTEs in Southeast China (south of 35°N and east of 105°E) associated with atmospheric anomalies are investigated. Two key domains in the upper level that are associated with HTE variation, the “exit” and the “tail” of the East Asian Jet Stream (EAJS), are identified. Poleward displacement of the exit is associated with warming tropospheric temperatures over East Asia and tends to be linked with high HTE frequency, while enhancement of the tail is associated with cooling tropospheric temperatures in the northern Pacific and tends to be linked with low HTE frequency. A possible reflection effect of the stratosphere on cool summers in Southeast China is proposed. Furthermore, these two domains are in essence two sectors of the phase-locked circumglobal teleconnection (CGT) pattern in the Northern Hemisphere. Linkages are found between HTEs in Southeast China and precipitation anomalies in the Indian summer monsoon region, and also in extratropical regions such as northeastern Europe. These teleconnections are set up through the CGT pattern associated with the westerly jet in the midlatitudes. These findings may be a source of variability and predictability of HTEs in Southeast China.