Abstract: The El Niño–Southern Oscillation (ENSO) represents the most prominent interannual signal within the global ocean–atmosphere system and stands as one of the crucial factors influencing the interannual variability of summer precipitation in the Beijing–Tianjin–Hebei (BTH) region. Based on data such as spring SST (Sea Surface Temperature), summer precipitation in the BTH region, and atmospheric circulation from 1961 to 2023, this study analyzes the interdecadal variation in the relationship between spring ENSO and summer precipitation in the BTH region as well as its possible causes. Results show that the key spring ENSO region significantly impacting the interannual summer-precipitation anomalies in the BTH region underwent an interdecadal shift in the late 1990s, migrating from the eastern Pacific in the earlier period to the central Pacific in the later period. Although SST anomalies (SSTAs) in the key spring ENSO region exhibit a strong negative correlation with the summer precipitation anomalies in the BTH region before and after the shift, the underlying mechanisms differ significantly. When SSTAs exist in the key spring ENSO region, the summer SSTAs in the North Pacific, Indian Ocean, and Atlantic Ocean show different characteristics, which in turn cause circulation anomalies in the tropics and mid-high latitudes through the synergistic effect of SSTAs in different regions. When the key spring ENSO region exhibits warm SSTAs, a distinct anticyclonic circulation is observed in the subtropical northwestern Pacific. After the interdecadal shift, this anticyclonic circulation strengthens, but it still fails to transport water vapor to the BTH region. The BTH region is controlled by a cyclonic circulation. In the earlier period, this cyclonic circulation is associated with SSTAs in the North Pacific, and in the later period, it is caused by the zonal wave train over the Eurasian continent, excited by SSTAs in the North Atlantic. The control of anomalous northerly winds over the BTH region reduces precipitation.