By using Ni〖AKn~D〗o 3 index，the summers during the different phases of the ENSO cycle are divided into four types Then based on the summer rainfall data of the Huaihe and mid-lower Yangtze valleys,using the cluster analysis method，we find that the developing(decaying) phase of El Ni〖AKn~D〗o and the decaying(developing) phase of La Ni〖AKn~D〗a belong to the same type.Then according to the different influences of the ENSO cycle on the rainfall over the Huaihe and mid-lower Yangtze valleys，a new East Asian subtropical summer monsoon index is developed.And by using of the index，it is found that during an ENSO period the interannual variation of the summer rainfall in the two regions is due to the interaction between the ENSO cycle and the summer monsoon.The ENSO cycle enables the rainbands position to change through influencing the range of the East Asian summer monsoon anomalies，however，the strength of the East Asian summer monsoon mainly changes the rainfall over the two regions.However，during the years without ENSO，it is the strength of the East Asian summer monsoon that mainly determines the rainfall in the two regions