Abstract: In this paper,a cold outbreak process(9-11,Nov 1979) has been analysed with dynamical diagnostic method.It shows that the decrease of the temperature in the cold dome moving to south is caused not only by the diabatic cooling on the surface but also by ascending adiabatic expansion.The mass divergence above the cold dome is caused by the strong positive vorticity advection combined with the maximun vorticity on the left side of the jet core.Thus,in the proceeding of the cold outbreak forecasting,we must pay more attention to the uniform of the wind speed distribution around the trough in higher troposphere,especially the behavior of the core on the northly jet stream behind the trough.