The climatic characteristics of precipitation over the middle and lower reaches of the Yangtze River Valley (YRV) during early summer of 2011 and associated causes are examined in this study. It is shown that, during May 2011, the precipitation over the middle and lower reaches of the YRV was below normal, but was above normal during June, and then droughtflood alternation occurs. This droughtsflood alternation is mainly influenced by the intensity of the South China Sea summer monsoon and the East Asian summer monsoon, and the abrupt northward shift of the western Pacific subtropical high (WPSH). During June 2011, there are two troughs located in the Arabian Sea and the Sea of Japan respectively, and a ridge located in the Lake Baikal over the middlehigh latitude Eurasian area. The frequent activities of northeast cold vortex (NECV) bring cold air masses to the middle and lower reaches of the YRV. At the same time, the WPSH extends to the west and north of its normal position, and shifts westward several times in June. It is indicated that it is just the interaction between the NECV and WPSH that leads to the reinforcement of the southwest lowlevel jet (LLJ) in the lower troposphere. The convergence between the northward warm and wet southwesterly flow brought by LLJ and the southward dry and cold air by NECV is favorable to the positive precipitation anomaly in the middle and lower reaches of the YRV.