Moist potential vorticity is used to investigate the influence of the blocking high position in mid high latitude of east Asia on the path of cold air action and thereby on the location of torrential rain in China in July,1998.Results show that when the blocking high lies in the middle of Siberia(the sea of Okhotsk),the torrential rain will likely occur in north and south China(western part of NE China,north China and Sichuan Plain);When the high is in Xiaoxin'anling and the subtropical high is north of its mean position,NE China will be likely suffered from torrential rain;when the high lies over the area centered at 55°N,135°E,the cold air action will be more frequent in the mid low reaches of the Yangtze River with the torrential rain there.