Defined is a new east Asian monsoon index ,which can perfectly describe the seasonal and interannual change of the wester n Pacific subtropical high(WPSH).On the basis of the index,the relations are discussed among the equatorial eastern Pacific spring SSTA,the summer WPSH and east Asian summer monsoon.Related to the warm(cold) spring SSTA in the equatorial eastern Pacific,the summer WPSH position lies to the south(north) of its mean,the west(east) of its normal,and is slightly intensified(weakened); the east Asian summer monsoon is also weak(strong),the mid/low reaches of the Yangtze River are hit by floods(droughts),accompanied by droughts(floods) in the south China and the Yellow River valleys.