Abstract:Based on the daily precipitation data of stations in China and NCEP/NCAR reanalysis data and using Mann Kendall method and period analysis, this paper analyzes the decadal variability and intra monthly oscillation of the ridge line position of the western Pacific subtropical high (WPSH) in autumn, and the possible connection with autumn precipitation over the upper reaches of Hanjiang River. The results show abrupt change of the WPSH ridge line in autumn happened around 1997, which is very different from the WPSH strength. After the abrupt change, the WPSH ridge line in autumn obviously moved north and the days when it stayed by north were more than before. Meanwhile, stronger intra monthly oscillation of the WPSH ridge line and increasing autumn precipitation over the upper reaches of Hanjiang River were observed. When quasi biweekly period is strong, it is more likely to be rainy in autumn over the upper reaches of Hanjiang River. Conversely when quasi biweekly period is weak, it is more likely to be dry.