Abstract: This study investigates the interdecadal variability of winter precipitation and associated physical mechanisms caused over the Three-River Source (TRS) region based on gridded CN05.1 and NCEP/NCAR reanalysis datasets for the period of 1961/1962–2017/2018. The results show that the winter precipitation over the TRS region experienced intensification in the late 1980s. The anomalous low over the Ural Mountains and the anomalous high stretching from Lake Baikal to Northeast China, which can be connected with the ocean–atmosphere interaction over the North Atlantic, alter the decadal changes. Specifically, after the late 1980s, warm sea surface temperature (SST) anomalies over the mid-high latitudes of the North Atlantic may have contributed to abnormal ascending motions, strengthening convection and triggering the eastward wave train, resulting in the anomalous low over the Ural Mountains and the anomalous high extending from Lake Baikal to Northeast China. On the one hand, the coincidence of anomalous low and high intensified and shifted the polar front jet southward, triggering upper-level divergence and development of convection over the TRS region. On the other hand, the anomalous easterly wind over the TRS, generated by anomalous high extending from Lake Baikal to Northeast China, influenced the decadal intensification of winter precipitation over the TRS by generating an abnormal convergence of water vapor flux. Furthermore, positive SST anomalies in the Indian Ocean can also have an influence on the interdecadal variations in winter precipitation over the TRS region by influencing the south branch trough.