The existence and causes of the recently observed rainfall heterogeneity over monsoonal east Asia in historical periods remain unclear. Here we show that such rainfall heterogeneity has been present at least in the last millennium, with decadal to centennial precipitation variations over southeast Asia and north China being broadly synchronous, while central to southwest China’s variations are generally out-of-phase with those in southeast Asia and north China. We propose that the western Pacific subtropical high, which reduces decadal to centennial precipitation over central to southwest China due to its anticyclonic feature, could be responsible for the observed rainfall heterogeneity over subtropical East Asia. Further analyses suggest that intensified decadal to centennial solar activity can lead to enhanced and northward and westward extension of the western Pacific subtropical high, resulting in tripolar rainfall heterogenous patterns over monsoonal East Asia.