Abstract: Based on the observations and NCEP reanalysis data, the authors analyzed to investigate the reasons resulted in the rainy and sunless weather in the middle and lower reaches of Yangtze River in late summer of 2014. The results showed that: the circulation anomalies were caused by abnormal large scale weather patterns, including the south Asia high, the western Pacific subtropical high and the east Asia monsoon. The location of south Asian high at 200 hPa was by southeast relatively to the normal, which was dynamically favorable for precipitations in the region; the polar vortex intensity at 500 hPa in the northern hemisphere was stronger than normal, leading to strong cold air masses intruding in China; both the western Pacific subtropical high and anti-cyclone circulation at 850 hPa were stronger and much by south and west to normal; two different circulation patterns in Eurasian mid-latitude displayed in the second half of August: period 1 (16-20), the pattern with two ridges and two troughs showed at 500 hPa, with meridional circulations much stronger than normal and more favorable for cold air masses to eastern China; the strong westerly flow over southern China at 850 hPa together with the subtropical high enhanced the southwest low level jet over the east China sea; period 2 (21-31), only one ridge and one trough circulation existed at 500 hPa with meridional circulation weakening, which was favorable for weak cold air reaching the middle and lower reaches of Yangtze River. There existed θse frontal zone, frontogenesis, up lift, mid-low-level water vapor convergence and wet tongue from the ground during the two periods, with all the physical elements much significant and consistent with the weather during period 1.