The decadal features of winter air temperature in northeast China and winter AO index and their relationship are investigated by using the monthly air temperature data at 160 stations in China,the AO index and the NCEP\NCAR reanalysis data.The analysis results show that they bear a significantly positive relationship on a time scale of decade.When the winter AO index was in a low(high) phase,the winter air temperature in northeast China underwent a successive cold(warm) winter.The possible mechanism through which the winter AO influences winter air temperature in northeast China is that at the ground surface when the winter AO index is in a low(high) phase,the Siberia high is strengthened(weakened),the winter monsoon over the East Asia is also strengthened(weakened),and northeast China undergoes a successive cold(warm) winter;and in the middle troposphere,when the winter AO is in its low(high) phase,the East Asia trough is strengthened(weakened),the ridge west and north of Baikal Lake is also strengthened(weakened),the circulation develops meridionally(zonally),the northerly wind is strengthened(weakened),and northeast China undergoes successive cold(warm)winter.