Based on TBB data from FY2E (2010-2014) and FY2G (2015-2016), the gauge-adjusted CMORPH hourly precipitation and daily gauge observations, statistical characteristics of eastward propagation of cloud clusters from the Tibetan Plateau (TP) and Mesoscale Convective Systems (MCS) embedded in these cloud clusters in the summers of 2010-2016 are analyzed. The results show that there are 120 eastward propagation processes accompanied with precipitation over the downstream region (east of 104°E). Most of these processes occurred in June, but those with longer durations more frequently occurred in July. Cloud clusters follow three prominent tracks to propagate from the TP to the middle-lower reaches of Yangtze River basin: 1. propagating eastward directly, 2. propagating along the Yangtze River, during which the cloud clusters first move southeastward and then turn eastward, and 3. propagating along complicated paths. The cloud clusters propagating along the second track has the highest impact due to their high occurrence frequency (46 processes), long duration and the most rainy days (heavy rain days) over the downstream region. The MCSs embedded in these eastward-propagating cloud clusters occur most frequently in July and more frequently over the eastern slope of TP, eastern part of Yunnan-Guizhou Plateau and the Yangtze River basin. The MCSs over the TP can only affect rainfall over the downstream region after they propagate eastward. This is because even the long-lived Meso-α Convective Systems (MαCS) with longer moving tracks over the TP or the eastern slope of TP cannot reach the region east of 110°E. The diurnal cycles of the Permanent Elongated Convective System (PECS) over different regions show that they propagate downstream more easily during the night. The MCSs embedded in the cloud clusters that follow the second track to propagate eastward are the most and also develop most robustly over the downstream region. They are highly associated with heavy rainfall events and areas affected by heavy rainfall.