The law in the variation of the subtropical high ridge line in July and the cause to its formation were analyzed in the paper. The results indicate that the location of the subtropical high ridge line has an significance low-frequency variation. The cycle period of its oscillation covers about thirteen years. The variation is characterized with a teleconnection structure at 500hPa in East Asia. The effective factors are mainly concerned with the apperence of the atmospheric blocking over the East Asia , SST in the region of block current, convective activites surrounding the Philip-pins and the subtropical high over the southern Indian Ocean.