By using outgoing longwave radiation(OLR) data from National Oceanic and Atmospheric Administration(NOAA),daily wind (850 hPa) data from European Center for Medium-Range Weather Forecasting(ECMWF) and tropical cyclones(TC) data from Joint Typhoon Warning Center(JTWC),the impact of quasi-biweekly oscillation(QBW) on tropical cyclone activity over the western North Pacific(WNP) is studied in this paper.The index of 10 to 20-day oscillation is defined by referring to the Madden-Julian oscillation(MJO) index proposed by Wheeler and Hendon(2004).The analysis shows that TCs always occur in the area where convection is active.During QBW-phase1,the southeasterly of the western North Pacific subtropical high is weakened by the anticyclone-circulation of QBW.The westward (northwestward) moving TCs tend to change their tracks to the west of 140°E.During QBW-phase3,with the southeasterly of the western North Pacific subtropical high strengthened by the cyclone-circulation of QBW,TCs tend to change their tracks to the east of 140°E.Case studies of some TCs are discussed in this paper.The results show that TCs may present sudden poleward track change while its center overlaps with the center of the cyclone-circulations (anticyclone-circulations) of QBW.