Abstract: This paper explores the modulation of quasi-biweekly oscillation (QBWO) on tropical cyclogenesis over the western North Pacific (WNP), using the Japanese reanalysis (JRA) daily data, NOAA/NCEP data and tropical cyclones (TCs) dataset obtained from the Joint Typhoon Warming Center. Through the classification of four phases, the composites indicate that the zonal wind and convective activity on 10－20-day scale propagate northwestward. During phases 1 and 4, the number and the occurrence probability of the TCs are lower. In contrast, the number of the TCs is relatively large and the occurrence probability of the TCs is higher during phases 2 and 3. Moreover, during phase 3, the number of the TCs landing in China is largest. From phases 1 to 4, the location of monsoon trough shifts westward over the WNP. The westward-propagating synoptic-scale disturbances due to the convergence of zonal wind on the eastern flank of the monsoon trough over the WNP are prone to translating to TD-type (tropical depression-type) disturbances, which is favorable for developing into TC by means of kinetic energy conversion from basic state in the monsoon trough.