A distinctive strong tropospheric cooling trend is found in East Asia during July and August. The cooling trend is most prominent at the upper troposphere around 300 hPa. Accompanying this summer cooling the upper-level westerly jet stream over East Asia shifts southward and the East Asian summer monsoon weakens, which results in the tendency toward increased droughts in northern China and flood in Yangtze River Valley. The observational evidences raise the possibility that the East Asian summer tropospheric cooling links to the stratosphere temperature changes and the interaction between the troposphere and stratosphere.