Based on the summer precipitation data of 400 meteorological stations in China, NCEP/NCAR reanalysis data, and NOAA SST (sea surface temperature) dataset from 1961 to 2016, the interdecadal variations of the relationship between the summer precipitation in the Huanghuai region and synchronous circulation as well as that between the summer precipitation in the Huanghuai region and SST of the last year are studied. The results show before (after) the 1980s, when El Niño occurs to the Pacific SST in the last winter, the summer precipitation in the Huanghuai region is less (more); before the mid-1980s, the relationship between the Indian Ocean Basin-wide (IOBW) of the last winter and the summer precipitation in the Huanghuai region is weak, while from the 1980s, the positive correlation is significantly enhanced. Further study shows when the Indian Ocean SST is consistently higher in the last year, the subtropical high in the geopotential height field at 500 hPa in summer is greatly enhanced, and such correlation after the mid-1980s is obviously stronger than that before the 1980s. On the sea-level pressure field, the area of higher correlation presents obvious Southern Oscillation mode after the 1980s, and the Indian Ocean SST strengthens its relationship with the summer precipitation in the Huanghuai region with interdecadal variations by affecting the key circulation areas which determines the summer precipitation anomaly in the Huanghuai region.