Abstract: In this paper, the process of the cold air invading the Qinling Mountains during January 20-22. 1977 is analysed with the observations and is simulated by the mesoscale atmospheric numerical model with a higher-order turbulent closure. The simulated results are basically identical with the observed results. Furthermore. by the numerical model. the dynamic mechanism of the Qinling Mountains screening the cold sir from the North is systematically discussed.