Abstract: In China，Daxinganling foehn results in a long"warm ridge" ,which stretches from 40°N to 52°N in the Northeast region ,in the distribution of sea-level average air temperatures in winter. Therefore.Daxinganling foehn seriously influences the climate of China. In this paper , a mesoscale numerical model，which has the ability to simulate the mesoscale mountain climates such as Boulder downslope windstorm in America ,is used. By using this model， the foehn on the eastern slope of Daxinganling Mountains in the Northeast China in the winter is successfully simulated. The cause of formation for this foehn is discussed,and the following con-elusions are obtained: (I)The Daxinganling foehn"warm ridge"at the east slope is due to the intense adiabatic sub-sidence of the strong downslope wind at the eastern steep slope. (2)The wave-breaking region over the Daxinganling eastern steep slope results in the strong downslope wind of the foehn., (3)The static hydraulic jump at the foot of the Daxinganling eastern steep slope makes the foelw occur only at the steep slope.

Key words: airflow over mountain, daxinganling foehn, wave breaking, Internal hy-draulic jump