Abstract: The summer weather in China is closely related to the subtropical high ov er the western Pacific (SHWP). The thermal contrast between the mid and lower latitudes could be the main factor to influence the strength and location of the SHWP. The first EOF mode of the sea surface temperature (SST) is derived and the correla tion of the SST and the SHWP is investigated by using the SST date and the geopo tential height and vertical velocity from NCAR/NCEP reanalysis dataset. Based on the above analysis two individual areas are selected. Then an index is defined to represent the difference of the SST (DSST) between the mid and lower latitude sover the Pacific. The index is highly correlated to the variation of the SHWP. The characters of the interdecadal variability of the DSST and its impacts on the SHWP are studied by statistic method and numerical simulation. It is shown that the variation of the SHWP is associated with the SST over two regions (30°-40°N，180°-140°W） and （10°S-10°N，140°-100°W） respectively. There is an abrupt change of DSST from weak to strong around 1976 which is closely relat ed with the change of the SHWP. When the DSST is larger, the SHWP is stronger, i ts domain is larger and can extend more westerly; when the DSST is smaller, the SHWP variation is on the opposite. The numerical simulations further show that i ncreasing DSST will result in the enhancing of Hadley cell descent and the stren gth of the SHWP. As a result, the DSST is one of the main factors to influence t he strength and location of the SHWP.