Abstract: The change of magnitude of the vertical zonal wind shear (MWS) in the western North Pacific is a very important dynamic condition for the genesis and development of the tropical cyclones with the weak MWS identified with a favourable condition. In this article, MWS in the western North Pacific is defined as the absolute value of the difference between 850 hPa zonal wind and 200 hPa zonal wind. The climatic characteristics of the MWS are analyzed. The results show that there exist two major spatial patterns of MWS in the western North Pacific. The first EOF mode shows an organized longitudinal pattern from the tropical Pacific to the subtropical Pacific. The spatial pattern of the second EOF mode displays opposite variations in the east part of to the west part of 140°E. We also investigate the circulation associated with the two spatial patterns. It is found that the first EOF is not only correlated with the low latitude, but also with the high latitude circulation in both hemispheres. The second EOF is mainly correlated with the local circulation in the western tropical Pacific and North Pacific. In addition, the time series of the first EOF mode is related with the equatorial sea surface temperature in the East Pacific and the tropical cyclone frequency in the western North Pacific and the time series of the second EOF mode is related mainly with the tropical cyclones frequency in the western North Pacific.