The development of the disturbance and stability of the time-averaged non-zonal basic flow in a baroclinic atmosphere are investigated by energy method. More attention is paid to the problems on the role of the meridional base flow to the development of the disturbance. The sufficient condition for stability and the necessary condition for instability of the time-averaged non-zonal basic flow are obtained from the generalized energy equation. With the axis of jet stream as the center, for the barotropic developing(decaying) disturbance, the perturbation streamlines must be tilting (on average) towards the upstream(downstream) direction of the basic flow on the horizontal plane.In the troposphere, for the baroclinic developing(decaying) disturbance, the perturbation streamline must be sloping upward and tilting (on average) towards the upstream(downstream) direction of the basic flow on the vertical section. The existence of the meridional basic flow will promote and strengthen the development of the disturbance, making the developing disturbance more unstable.