Abstract: Based on the Northeast China cold vortex (NCCV) case calendar provided by the Liaoning Meteorological Bureau, ERSST V5 sea surface temperature data, and NCEP/NCAR atmospheric reanalysis dataset from 1979 to 2021, this study examines the association between late-summer NCCV days and early-summer tropical Indian Ocean (TIO) sea surface temperature and its temporal stability. Results show that the strongest positive correlation between late-summer NECV days and preceding TIO sea surface temperature occurs in early summer. That is warm early-summer TIO sea surface temperature anomalies tend to be followed by more late-summer NCCV days. However, this linkage is non-stationary and the significant positive correlation becomes statistically insignificant after 2004. The abrupt shift is attributed to an eastward displacement of the late-summer TIO warming and corresponding atmospheric response to the early-summer TIO warming. During 1989-2003, the early-summer TIO warming persists into late summer, exciting eastward-propagating Kelvin waves that reinforced anticyclonic anomalies over the western North Pacific. Low-level divergent flow anomalies associated with the anticyclonic anomalies over the western North Pacific converge markedly over Northeast Asia, inducing the mid–low-tropospheric cyclonic anomalies and negative geopotential height anomalies that increase NCCV days. By contrast, during 2004-2017 the eastward shift of the late-summer heat source precludes significant anticyclonic anomalies over the western North Pacific, thereby weakening the association between late-summer NCCV days and early-summer TIO sea surface temperature.