Western China is a highly climate-sensitive area, over which anomalous precipitation plays an important role. In this study, the temporal and spatial distribution features of winter precipitation over Western China are analyzed. The results show that the primary mode of winter precipitation over this area showed a homogeneous change and it underwent a significant decadal change around the mid-1980s, after which winter precipitation suddenly increased compared to the amounts before. Analyses of atmospheric circulation and water vapor transportation indicate that different factors influenced decadal variation and inter-annual variation of winter precipitation over Western China. The main cause for the decadal variation was westerly water vapor transportation at mid-to-high latitude; while the primary reason for the interannual variation was southwesterly water vapor transportation from the Arabian Sea. In two different decades, the channel of water vapor transportation for winter precipitation over Western China was consistent. These findings indicate that prediction of winter precipitation over Western China should be studied on different timescales, and it would be more reasonable to synthetically consider the interannual variation, decadal variation, and even long-term variation in climate predictions. In addition, the consistence of interannual influential factors in different decades provides a scientific basis for development of a stable interannual prediction mode for winter precipitation in Western China.