ENSO event occurring in winter—spring greatly influence the following summer weather of China. When the Southern Oscillation (SO) in winter—spring is weaker and accompanied with ENSO, it will lead the west Pacific high (WPH) in the following summer to strengthen and extend westward through the action of enhanced Hadley cell located in mid–equational Pacific. And the location of the ridge line of WPH in mid summer (July—August) and the monsoon rain belt in eastern China in the northern side of WPH are controlled by two factors, both the preceding SOI in late spring and the direct solar radiation (S) of clear sky indicating the stratospheric volcanic dust content. Owing to the significant annual variation of S, the difference of location of the monsoon rain belt in eastern China in mid summer will be considerable during the ENSO periodes. Based on this analysis, the seasonal forecast for the summer rainy tendency in the mid–lower valley of Changjiang river and Huaihe river in 1987 (ENSO year) has been made.