On the basis of the fact that there exists significant negative correlation between temperature and precipitation over the southeastern China in summer, a drought index is a ppropriately chosen to investigate the spatial and temporal variability of summer drought/flood while no long-lerm trend is found in the time evolution of drought/flood, structures of four spatial patterns based on the index are more signatures of similarity than precipitation patterns, and reflect the climate a nomaly. In addition, singular value decomposition (SVD) is applied to analyze the index dataset and 850 hPa U, V components and some other fields, respectively. It turns out that drought likely occurs in the middle and lower reaches of the Yangtze River when westerly over the South China Sea and the Philippines, southerly over eastern China, and westerly (easterly) over the north (south) of subtropical high increase. On the contrary, flood likely occurs.