Abstract: Using the operational prediction model (B Model) of Beijing Meterological Center,we do some of numerical experiments of crossing and rounding.mountains in all velocity ad justment scheme.We study dynamic effect of Qinghai-Xizang Plateau and Rocky Mountains on the lee cyclones.The results,shpw that due to air flow round Qinghai-Xizang Plateau,divergence is distributed in the shape of confluence which match cyclogenesis area and cyclonic track in the east Asia.In the downstream of Qinghai-Xizang Plateau,convergence of high level of troposphere restrains cyclone development in the east of China continent.1n the Northern America,air flow primarily crosses over Rocky Mountams.Air is adiabatically cooled when it flows upward in the west flank of Rocky Mountains,while air is warmed when it flows downward in the lee side of Rocky Mountains.The fact is important for the lee cyclogenesis and the lee frontogenesis of Rocky Mountains.Air flow crossing over Rocky Mountains is also main cause for forming dryline in the mid-west of United States.