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As shown in comparisons of the characteristics of inter-annual and inter-decadal variability and periodical changes in the number of tropical cyclones forming over the western North Pacific by three major forecast centers,i.e.China Meteorological Administration (CMA),Regional Specialized Meteorological Center of Tokyo (JMA) and Joint Typhoon Warning Center (JTWC) of Guam,there are the following important points.(1) Climatology of tropical cyclone (TC) or typhoon (TC on the intensity of TS or stronger) shows some difference in tropical cyclone frequency among the centers,which is more notable with TC than with typhoon.Both of them are more at the database of CMA than at those of the other two centers.(2) The difference is too significant to ignore in the inter-annual variability of tropical cyclone frequency between CMA and JTWC,which mainly results from the obvious difference in the inter-annual variability of the number of generated tropical depression (TD) between the two databases.The difference is small in the inter-annual variability of TS formations among all the three databases,and consistence is good between JMA and CMA or JTWC.(3) Though differences are not significant in the periodical variation of TC formations between CMA and JTWC,they are markedly apart in the inter-decadal variability,which is mainly shown by an anti-phase during the 1990s.(4) Non-homogeneity may exist around the late stage of the 1960s in the data of tropical cyclone frequency.