Based on the ERA-interim reanalysis data of the ECMRWF(European Center for Medium-Range Weather Forecasts) from 1979 to 2013,this paper systematically analyzes the intraseasonal variation of winter meridional wind in East Asian monsoon region and its possible mechanism by using the mean square analysis,power spectrum analysis,Butterworth filtering,synthesis analysis and other statistical methods.Results show that the winter meridional wind anomaly of East Asian monsoon area significantly changes in South China area,with an oscillation period of 10-20 d (Quasi-BiWeekly Oscillation,QBWO).In the horizontal direction,the 850 hPa anomalous north wind has the characteristics of propagation from the high latitudes to the low latitudes.The anomalous meridional wind near 60°N spreads southeastward,and the anomalous weak meridional wind near 30°N spreads eastward in the subtropical zone.They converge in South China,then are divided into two centers,which continue to spread southward and eastward respectively.The oscillating evolution of winter meridional wind has the characteristics of anti-phase between Lake Baikal and South China.There exists the energy conversion from the basic air flow to the quasi-biweekly fluctuation in South China,therefore the anomalous meridional wind will enhance significantly there.In the vertical direction,the anomalous meridional wind exhibits strong-weak-strong anomalous center features in the upper,middle and lower layers of the troposphere.There is a large center of meridional wind in the lower (850 hPa) and upper (200-300 hPa) layers of the troposphere.However,the quasi-biweekly oscillations of meridional wind are relatively weak in the middle troposphere.Rossby wave changes significantly at 300 hPa.Over the eastern part of China,there is also a large value center of meridional wind with quasi-biweekly oscillation period.The fluctuations in the subtropical regions at 300 hPa are more obvious than those at 850 hPa,and the fluctuations near 60°N move southeastward,similarly merging in the eastern part of China.The Rossby waves from Europe spread eastward and the Rossby waves from North Pacific spread westward,and their convergence near the eastern part of China results in an increase of fluctuation energy.