In the present study,based on the NCEP/NCAR reanalyses dataset and best track data of the typhoons provided by China Meteorological Administration(CMA),the influence of the Australian cold air activity on the genesis of tropical cyclones(TCs) over the western North Pacific was investigated.It was found that,off the northeastern coast of Australia,the occurrence frequency of the meridional wind larger than 6 m/s was the largest(50 days annually).Therefore,the Solomon Sea was determined as the key area of influence of the Australian cold air activity on the low latitudes in both hemispheres,and a cold air intensity index over Australia was defined by the low level meridional wind over the Solomon Sea(SSV).The SSV was shown to be closely related to the cross-equatorial flows and westerly over the Equator,as well as the SOI.As the SOI becomes weaker(stronger),the SSV becomes stronger(weaker).The location of the tropical cyclogenesis(TCG) over the western North Pacific coincides with the variation of the monsoon trough during the years of strong and weak cold air activities over Australia.However,the total TC number has no significant correlation with the SSV.The monsoon trough over the western North Pacific is stronger and located more eastward than normal,and the location of the TCG is more eastward and southward than normal during years of strong cold air activity.Meanwhile,the monsoon trough is weaker and located more westward than normal,and the location of the TCG is more westward and northward than normal during years of weak cold air activity.The distribution of vorticity in the lower troposphere,the moisture transport,the vertical shear of horizontal wind and the convections in low latitudes all indicate that the locations of the TCs over the western North Pacific are more eastward and southward(westward and northward) than normal during strong(weak) years of cold air activities over Australia.