Abstract: Based on the tropical cyclone data from China Meteorological Administration (CMA), the sea surface temperature monthly data from National Oceanic and Atmospheric Administration (NOAA) and the monthly reanalysis data provided by the European Center for Mediumrange Weather Forecasts(ECMWF) for the period of 1958-2001, the influence of the vertical wind shear variation on interannual changes in the tropical cyclone (TC) activity in the western North Pacific was examined. It is found that there exist strong negative correlations between occurrence frequencies of TC the whole/TSTY (all the TC with the maximum sustained wind equal or greater than 17.2 m/s)/WTY (including typhoon, severe typhoon and super typhoon) and vertical wind shear in the western North Pacific （WNP, 5°-30°N，110°E-180°）. Such an effect is not significant for the TCs initiated in South China Sea (5°-30°N, 110°-120°E) and the western part of the WNP (5°-30°N, 120°-150°E), while the TC frequency of the eastern part of the WNP (5°-30°N, 150°E-180°) varies remarkably according to vertical wind shear. In the weaker vertical wind shear years, TC frequencies in South China Sea and the western part of the WNP are not very different from those in normal years, while the TC number of the eastern part of the WNP is much larger than that in normal years, which makes the total TC number in the WNP being larger and causes the average original location to shift more eastward than the normal. In stronger wind shear years, the statistical results are reverse. Furthermore, the effect of vertical wind shear on the TC annual frequency and the position becomes more significant for stronger TCs. At last, the difference of climatic environmental field between weaker vertical wind shear years and stronger years has been compared. In weaker vertical wind shear years, the monsoon trough is more vigorous and extends eastward to the 160°E, and the vorticity and convergence in the lower troposphere, as well as the divergence in the upper troposphere are all enhanced significantly over the warmer ocean. These environment conditions are favorable to the TSTY genesis in the WNP, which results in a larger number of TSTY during weaker vertical wind shear years. The largest difference of these environmental conditions between weaker and stronger wind shear years is in the eastern part of the WNP, which is an important reason causing the eastward movement of the genesis location in weaker wind shear years.