This paper explores the modulation of 30－60 day low frequency oscillation (MJO) on tropical cyclogenesis over the western North Pacific (WNP) in terms of dynamics and energy conversion, using the global reanalysis data and tropical cyclones (TCs) archives obtained from Joint Typhoon Warming Center, USA. During the westerly phase in the western part of the WNP, waves in the flow convergence region are characterized by the increase in wavenumber and the decrease in wavelength, which causes the evolution from large-scale waves to synoptic scale ones. The convergence and shear of zonal wind in the westerly phase would accelerate kinetic energy transfer from low frequency to high frequency, favorable for TCs formation in that region. Reversely, tropical cyclogenesis would be inhibited during the easterly phase. In addition, the TCs occurrence probability would increase (decrease) with the strength of westerly flow during the westerly phase (the strength of easterly flow during the easterly phase). However, the modulation of MJO on TCs would weaken in the eastern part of the WNP. The interannual variations of MJO activity suggest that, during the warming state years of the WNP warm pool, MJO is active and the westerly phase is prevalent, which is conducive to tropical cyclogenesis. The circumstances are reversed during the cooling state years of the warm pool.